[Simlasa]

GURPS having all those great setting books, and some of the licenses, like Conan, certainly caused me to buy a lot of their books.

As for Hero, I certainly don't think they'd be in the position they are if they hadn't had Champions... and yes, it's a genre... but to me that's splitting hairs a bit... people I know started playing Champions because they wanted to play superheroes... they stuck with the Hero system because they knew the rules and they didn't suck bad enough to drive them out (I'm not saying the rules suck by the way).

I know very few people that shop for games based on rules first... setting/genre second... 'let's go down to the game store and see if there are any new dice-pool systems out!' No, people pick up the game because the cover looks cool, it has an interesting name, the blurb on the back of the book sounds cool, the interior art gets their imagination going...
I can't ever remember picking up a book that looked great from me and then thrusting it back on the shelf because it was 'roll over' or some other mechanism I don't care for (not saying I don't care for roll over either).