You're assuming that the average consumer can even tell the difference. I have several friends who've tried my SR-404 rig and couldn't tell the difference between that and stock iPod earbuds.
Let's eliminate sound quality and consider other factors, and compare some cans.
Let's say Grado SR-60 vs stock iPod earbuds:
1) Comfort - earbuds win; they're not ideal but they don't clamp on your ears like Grados do.
2) Portability - earbuds win; they're 1/10th the size.
3) Practicality - Grados will leak sound everywhere, and need to be cuddled and protected, lest something breaks. The buds don't care.
4) Looks - with the white buds, you're an iPod person, you're cool. With Grados, you're a geek.
5) Price. Ultimately, it all comes down to this. Why spend money on another headphone when you already have one for free? Remember, we can't tell the difference in sound here.
So, seems to me like the buds are 5 for 5...
This isn't far-fetched, this is the logic that my friend used on me. The same friend who lives in a manshion, just bought a $6000 pool table for one of his rec rooms, and could afford Wilson WAMM's if he actually cared about it. He'd rather waste money on a new Lexus (his old one is a few years out of date).
We're a niche group interested in a niche hobby. I'm sure there are more people out there that are interested in fishing lures.
[Edit: the only real advantage for the mainstream consumer out of any gear that we would like is in the isolation that canalphones provide. Hence, you actually see Shure and Etymotic products advertised in iPod related stores. However, canalphones are fussy - which is why noise cancelling is big and they're not].