Because they're still damn good games, even after all this time and all these iterations.

Every game keeps the basics the same, while adding new stuff to mix up and enhance the gameplay, ie. Gold/Silver split the special stat in two and breeding to transfer moves, the third gen added natures, the fourth gen separated move types from their element - ie. normal attacks can be both physical and special, etc.

Pokemon is one of the best, and probably the most consistent (strategy) RPG series in terms of game quality.

New Pokemon, new routes, new moves...

Although, i would like a Pokemon JRPG on the Wii...

I buy them cuz to me they are still fun

 Exactly.  If I, as a non-sports gamer, look at NHL 2001 and NHL 2009, I see essentially the same game--it's a hockey game.  However, it's the minor improvements in each version that keep people coming back.  Along with the hundreds of new monsters, of course.

People don't buy all of those. You know fully well many of those are actually the same game with a slight variation in Pokemon type to enhance the trading aspect of the game. Here's a realistic way of looking at it.

Gameboy-Pokemon Red/Blue/Green/Yellow(Director's cut)

Gameboy Color-Pokemon Gold/Silver/Crystal(Director's cut)

Gameboy Advance-Pokemon Rub/Sapphire/Emerald(Director's cut)

Gameboy Advance-Pokemon FireRed/LeafGreen(Remakes of the original Pokemon Red/Green for the GBA)

Nintendo DS-Pokemon Diamond/Pearl/Platinum(Director's cut)

4 main games and a remake.

I'm not a big sports gamer, but I am a football fan. I would never play Madden 2007 because the teams are simply not the teams they have today. If I play those games (I usually rent one every once in a while) I need to have the most up-to-date version, or it just feels stupid.

Pokemon, while not quite the same, is similar (the old games are still quite fun). I want the new moves, the new features, the new Pokemon. And it's always a great game, even if the basic gameplay remains the same. Why fix what isn't broken? Of course, I would LOVE an epic, massive, 3-D Pokemon adventure, but the original formula works, and it works very well. It is a good game. Even a 3-D version would still need to retain as much of the original gameplay as possible.

If you don't like the game to begin with, then it's true, you will have trouble understanding why people want to get the new games every time. But for those of us who loved the first, the new games continue to deliver a quality experience and never fail to disappoint.

that's a nice point you got there, nintendo sure does know how to create succesfull series

because they got catch'em all

Wait.... wait... what?

Onyxmeth.... there was a Pokemon Green at the same time as Red/Blue? Why was I not informed of this? I always thought I was a cool kid because I was one of the few (in my clique) who had Yellow, and everyone else had Red/Blue.

If I had Green, however.... I could have disposed of those other Yellow owners.

My childhood cool-ranking was cut short because of ignorance, drole.

Because new children are born everyday.