Hmm, they're taking it a step further than Blizzard did with WoW. Base game comes with all expansions but the current one, but you're still paying for the base game (plus monthly sub if you don't make enough gold in game). I find GW2's approach intriguing.
I'm amazed it's been keeping them financed for so long. They deserve it, but I didn't think they'd get it.
Guild Wars 2 is probably the best MMO that I don't play anymore! They have a penchant for randomly invalidating my password about every three months and forcing me to jump through hoops with their support system to get my account turned back on, therefore I just don't bother with it anymore.
So far I'm liking it, and the only thing I notice that tells me it's not a 100% paid for game is the little link in the upper left corner that says "upgrade your account". Aside from that, I'm not noticing any drawbacks. It's taking some adjustment, though. I played WoW for years, and this system's a bit different.