I just think they've made a bad call. Unreal Tournament 2003 is just too long winded, doesn't roll off the tongue, and creates more confusion. Think of a new PC gamer in September 2003 - wow Unreal Tournament 2003 - I've always heard about Unreal - I think I'll give it a try it must be new, and two months later Unreal Tournament 2004 is released. Damn, my games out of date!
Think of the parents as well. Especially ordering over the 'phone.
And lastly, Unreal Tournament was based on 2291 or some such far future date, so Unreal Tournament 2003 sounds like a game based around 2003... not so much confusing, but lacks cohesion to the game underneath the long title.
/* thanking god for cut and paste */
Regards,
JCC