Remember BF1942 takes place over small maps with only a small number of players (max 64, but anything over 50 lags big style).
BTW, that game has improved hugely in the last few patches. I don't know how you get 5 FPS. I have a 1.2 GHz Tbird, Geforce2 Pro 64 and 512Mb RAM and it runs smoothly even with high detail and lots of action on screen.
Also I think it has the best sound implementations of any game I've seen. Better than WW2OL by a mile. You can stand on a hill-top and watch the tracer and hear the delayed high fidelity sounds of explosions, MG fire and sub machine gun fire. It's very atmospheric.
AH was going to have a FPS aspect with regards to bunker combat - i.e. the taking of fields. This has been post-poned until next year I believe, with the advent of AH2.