Well, to be honest, those aren't really compelling enough reasons to change the current system.
Tise1983, you joined up 2 weeks before I did, and yet I don't have any kind of problem keeping track of the game worlds. Maybe if you (general you) are still in the begginer worlds, which really ARE short, then yeah, you might lose track, but when you consider that the normal worlds can take last anywhere between 6-12months if not more, then it really isn't that hard to track.
On that same note ZombieSlayer, achievements are tracked with the world number and the date achieved, I really don't see any real reason why it has to specifically be game world XX, when the date is all you really need. Tbh, I feel that the game world stat isn't really relevant at all, and mostly just serves as an addition "bonus" stat, as it were. As for saying back in GW XX I did this, i can maybe somewhat understand that, but again, I don't really feel that it's relevant what game world is, especially since anybody who is a newer player than you will have no concept of the GW you are talking about.
There's also good reasons why it shouldn't change. For example, if a new player comes and sees all the game worlds in the double digits, they are going to be disheartened and not motivated at all to join the game. They might feel that the entire game is either over-populated or that there's way to many advanced players to even bother competing with. I would have felt the same way, and would have never joined if I found the worlds in the double digits. I do want to point out that yeah, now I know that it wouldn't work like that, but as somebody seeing the game for the first time, they won't know what to assume.
I also want to just add that i'm not being critical of you guys, I just feel that any reason to change the Game World numbering would have to be more than just simply personal preference. Most numbering/organizational system are arbitrary anyway, and if a new system doesn't offer some kind of advantage over the old system to the person implementing it (meaning Sami), then there's no reason the system should change.