In my opinion, a lot of this is tied up with the marketing of tarot decks. Many people say that it is AT that made them want to buy decks. That's certainly true for me.
Partly it's the information available, scans and reviews and testimonials, which is very cool.
There's also encouragement aka social pressure that comes from feeling part of a group all clicking "buy" on various web sites and reporting with glee what they're waiting for from amazon.com or e-bay.
Don't we figure, these people might know something I don't know? Okey dokey, I'll buy...
I sometimes get the feeling that we're "supposed" to love certain decks because a lot of other people say they do. I guess this is unavoidable if you pay attention to what other people say and what's the point of being on a forum if you don't
So buying turns into a social activity, not just an individual decision.