I have a Wii and a PS3. I could have owned an Xbox360 but I chose the other two. I'm a retired game junky. I'm at best casual. I think there may well be another category for people like me who shouldn't even be considered casual.
I bought the Wii because my wife LOVES Mario games and I knew she could play every single one every made plus the new ones. My kids (4 and 2) would eventually be able to play Wii games with the game extensions which lo and behold...they CAN! Outdoor Adventure and Wii Fit both have platforms which do not require using a gamepad/wiimote meaning my entire family can play together. The Wii is tons of fun and playing Resident Evil 4 was one of the most eye opening experiences in my gaming experience. On pure fun factor it DESTROYS every other game I've ever played. Why? That dang Wiimote made it spectacular. There is a reason this game is often ranked in the top 5 games ever made, particularly the Wii one.
Yet, despite the fun I was having with the unit I wanted something more. I was getting tired of upgrading my PC every time I wanted to play a new game (I have a 30" monitor so my video card(s) have to be really up to the challenge). So I made a decision to stop the PC upgrade cycle and stick with console gaming. The choices? Xbox360 with bigger library, many cool exclusives and friends who work at MS and can get games free or for dirt cheap. OR.... PS3, more costly upfront, not as many exclusives and not as much access to free games or cheap games. I do have a single friend who I can share games with but ultimately I was going to pay through the nose for anything I wanted.
I went with the PS3.
Why? Hardware.
Why? Media capabilities.
Why? Linux.
Why? Games.
Why? Blu-ray.
As a geek, and a computer scientist, the hardware of this thing is just hands down the coolest little unit to come into the home in a long long time. Developing for this is great and the capabilities that have already been listed in this thread are legion. A supercomputer in my basement! String a few together and I have my own powerful protein modeler. Run just one and I share my cycles with Folding At Home.
As a husband and father, the media capabilities of this sweet unit, out of the box, are better than the Xbox. Wi-fi? Check. HDD? Check. Ability to read from my server? Check. Save money by not buying Squeezebox? Check. Terabytes of music. Terabytes of our DVDs all online all ready at the click of a few buttons on the bluetooth remote. AWESOME. OUT OF THE BOX.
Linux. Nuff said right there. A full on OS in my living room with little more effort than a single partition and loading up a USB drive. bluetooth keyboard and mouse and my family can surf and not touch daddy's computer. AWESOME!!!!! Also, I can tinker around with my full on computer in my living room. Very very nice.
Games. Now, many may be thinking...see Zanth, this one is 4th on your list not first and it should be first because we are talking game consoles. You know...for the most part you are right, and that argument wins hands down when I look at the Wii. But because the PS3 is so much more and I'm a computer geek, the other factors weighed heavier. Also, because the games for the PS3 are not as family friendly (though Little Big Planet may be the best game ever) and I don't have a lot of time to game...it does fall into 4th place, but don't think 4th is such a bad thing. I still bought it and the Xbox likely will never enter my home. So 4th in this case is still grand!
So back to games...the exclusives are why I went with it believe it or not. Two words: Team Ico. I bought the 60GB unit because it had full hardware support for PS2 games. I went out and bought Shadow of the Colossus and ordered up Ico. I had heard these were games for more mature gamers who favoured a solid/mysterious story with a unique gameplay. I was not let down and I can only imagine what this company has in store for a PS3 game.
Here are three more words: God of War. The best action/adventure series I've ever played. Total mayhem, total fun...totally exclusive to Play Station.
Two more words: Final Fantasy. So yeah...XIII won't be exclusive to the PS3 but when I bought it no one knew that yet
Last two words: Playstation library.
Sure, those that had a Playstation 2 already may not have considered this a factor but I hadn't played a console since the Super NES and so I had before me, more games with the Playstation 1 and 2 than going with the Xbox family of games. Ultimately for games, if I were younger and playing a lot more with my friends online, I may have gone with the Xbox because of Gears or Halo, but frankly, I never got into Halo and believe me I tried to. Gears has been a ton of fun but not enough to really keep me interested. For online gaming...if I really want to that badly, I'd default to the PC again. Far more immersive for me. Anyhow, I just didn't feel the Xbox necessarily bested the PS3 itself for games and the catalogue of games available to me dwarfed the Xbox's options.
Finally Blu-ray. The best Blu-ray player on the market and perhaps will only be surpassed by the likes of Denon with their $5000 units. $500 or $5000 for a stunning new media player? I'll go with $500. Although I'm not an avid movie collector (why bother when my father-in-law owns 10 000 DVDs, yes TEN THOUSAND), I'm not so into buying movies and unless a movie will really merit hi-def, I won't go and replace it. Yet, at some point I will buy an HD TV and Blu-rays will be enthusiastically appreciated. So a built-in blu-ray drive alone is worth a costly price hike and the move to PS3 vs. Xbox.
The PS3 out of the box (at least when I bought it) came with far more than the Xbox and if the Xbox were to compete, I would have had to buy add-ons which would close the gap between the two in price. I wanted what I wanted and I think PS3 was hoping more folks would be in my situation, seeing the PS3 as something MORE than a gaming console. They wanted it to be the be all and end all of entertainment systems, they wanted it to be the main hub. Apple be damned with your crappy TV thingy or your sub-par mini (though I really like the Mini), they felt they could get in there with something insane and it would work because of Blu-ray and because of the Playstations past success in gaming. They may have overstated their target outcomes and they may have overpaid for their product, requiring a really high selling price, but ultimately they may have made one of the most incredible consumer devices EVER.