FLAC vs MP3 320? Depends on the cans and the material
LOD vs Headphone Jack? Depends on the device and the jack
FLAC vs MP3 256? Depends, but I can with some consistency
Amp vs Unamped on headphones with under 50 impedance? Depends on the cans and amp
Sources (Laptop vs portable)? Again, depends on specific sources
Absolutes can be rather silly, they tend to close your mind to possibilities.
I was talking about the iPod touch and iPhone, possibly the two most commonly used MP3 players in the world. Sansa shouldn't be too far behind but that's one of the few exceptions where the weaker audio output would justify an amp with line out. But if you can afford a decent amp, why not just get iPod or one of those mighty Cowons? They don't need amps for most portables...
Sources: Of course, an Alienware with 5.1 surround would have a better sound card than a $400 Acer, but for people with the average $600-700 laptop?
Possibilities generally turn out to be placebos
A lot of "big" differences audiophiles talk about are actually pretty subtle. Audiophilia is all about subtleties, because in the long run, if you listen to music for a few hours every day, even the most subtle differences... can make a big difference in the long run.
I agree on the other parts, but music isn't something that's cumulative, like weightlifting. While you can say that the extra X amount of pushups add up after every workout, it's not like listening to the same thousand or so songs (average music library) collects inside of you, and will add up to something over an amount of time.
After a bit of thinking, I feel that the people with the most influence on Head-Fi have the most advanced gear and perfectly trained ear to test audio. The extra .xx9 digit of hundred dollar silver line cables might somehow improve audio in the ideal situation with perfect gear, and those audiophilles give praise to the accessory as being helpful. In turn, followers of the well known audiophile will think that "cheap(er than getting a better set of headphones)" upgrade will give them better sound to their sub-$1000 gear, when instead, the bottleneck for sound quality lies elsewhere. It's like you have an old, standard clocked Pentium 4 in a standard computer setup. Getting another 6 GB of ram won't help whatsoever when you already have 6, because the bottleneck to speed is in the processor itself.
Entering the world of Hi-Fi also comes with it's problems similar to being a doctor. Before I joined the forums, I was completely satisfied with my pair of iBeats and enjoyed my music immensely. As I explored into the depths of Hi-Fi, and like a doctor walking around in the world, I hear small problems just as the doctor would see severe symptoms and conditions which other people would not notice. I would spot problems everywhere, and like the doctor, I can never get this "world" to be as "healthy" as I can. Head-Fi has taught me to actively seek out what's "wrong" with my music quality, and get irritated by what before would never had been an issue...
Wow that was a long post...
TL;DR: Music Listening isn't cumulative, Average Head-Fiers are mislead by people with expensive gear praising expensive components, and the pursuit for Hi-Fi let's you see more problems than before, pushing you into an unending cycle of upgrading until you reach sonic perfection (which by the time your ears are probably worn out)
TL;DR was TL;DR: Audio Gear is imperfect, and perfection is pretty damn expensive
TL;DR: Too Long, Didn't Read (My opinion for so many posts on this website)
EDIT: Yes, those fancy shennanigans could make a difference on the ultra-high end of the spectrum, but the audience mainly people with sub-$500 rigs, and money is wasted on getting those $100-$200 cables, which would be "Cheap" when compared against the multi-thousand dollar gear they're designed for. Example would be some grado-pads I've seen a while back. The headphones were in the high 500 hundred or so, and the pads were $60. $60 for some headphone pads, but it's really not that much when compared to the $500 headphone. But if people with the 80 dollar SR60i get pads that are almost as much as the headphone...?
Edited by Xinze - 4/10/12 at 10:08pm