Some people lack the knowledge and skills needed to be able to buy something from Amazon. Compare buying something from Amazon with buying anything using Bitcoins - Amazon is ridiculously easy.

Bitcoin will never reach that level of ease of use. But when it has something like a 5 step LiveCD[1] it might start to get wider use.

[1] Something like insert CD, prepare anonymising stuff; load encrypted file from USB stick; load key from hardware token and enter short password; and have the distro wallpaper give idiot proof flowchart diagram instructions.