1440 * 900 = 1,296,000 (Native resolution, 17" and 19" widescreen)
1280 * 1024 = 1,310,720 (Native resolution, 17" and 19" standard aspect)
Widescreen monitors don't have higher resolutions or larger screen sizes, but for most people they offer better screen real estate just because stacking windows left-to-right is more natural than top-to-bottom. Movies and 16:9 TV shows also fit better.
And apparently, new games all support widescreen. I don't have any new games, but I'm sure someone else can tell you more.
I have BF2 set up to play in 1440x900 even though that's not one of its set resolutions, but I haven't figured it out for AVP2 yet. The only reason I can think of to get a 4:3 monitor is if you play a lot of older games.