DAT tapes are a world away (in price as well as quality) from the crappy 'cassettes' foisted on us in the 70s - if vinyl cost a dollar per platter, you can bet the record companies were ecstatic when they could do cassettes for 50c each. Nothing like the sinking feeling that accompanied the tape breaking or, worse, getting tangled in the heads of your car's player. I realise that many here would have had better kit (and cleaned the heads religiously), but as an idiot-proof medium its hard to go past the ipod-plugged-into-the-car-stereo.
As for reel-to-reel, that's like comparing an F1 car to a Yugo : sure, they're both cars, but that's where the similarity ends. If you have the Beatles masters in your garage, more power to you, but that has little to do with 'cassette tapes' as I understand the term.
http://en.wikipedia.org/wiki/Cassette_tapes
While ubiquitous and accessible, cassette playback suffered from flaws frustrating to both professionals and home recording enthusiasts. Tape speed could vary between devices, resulting in playback pitch that was too low or too high. Speed often was calibrated at the factory, and could not be changed by users. The slow tape speed limited fidelity and tape speed consistency, resulting in poor wow-and-flutter. Different tape formulation and noise reduction schemes artificially boosted or cut high frequencies and inadvertently elevated noise levels. Sometimes, a player (especially in a car radio) could damage the tape, rolling it around the capstan axle or its pressure roller, winding several feet of tape into the mechanism.