I'm having the same issue as you with wi-fi on the 4G.
Due to where we live the 3G network connection is faster than our actual broadband connection and since purchasing in March, most of the time we have not used wifi only for browsing the internet etc.etc - costs are high and after a few steep bills in early June I removed the SIM and reverted back to wifi only use in our household - since then nothing but problems with wifi dropping or weak signal when compared to our iTouch 4th generation.
I've only now found this thread, but after more than two weeks of this, my daughter who likes children's online gaming is getting very annoyed with continual lost/dropped connections when the iTouch is working just fine.
I'm running a Netgear 3500 duel band system - last years topend model, and the latest Airport Extreme the iPad 4G is acting the same on both routers - have tried the fixes recommended on these boards with no luck - the iPad was one of the first off the Assembly line - I understand the iPad3 wifi only version were having early problems.
Basically, have I got a lemon and should I get Apple to swap with a replacement having spent more than 24 hours of my own time trying to remedy the issue?