Strange, wifi is normally more power hungry then gsm...
Could be the processor spending more time rendering and the screen being up for longer (waiting for the slow page to load) that kills the battery. I know setting my phone to check email every hour hasn't really affected the battery life.
Well I just got back from the Apple store. My iPhone was crashing even after I did a couple of restores on it.
I walked in, told the Mac Genius my problem and he handed me a new iPhone in 5 minutes. That's the way to treat a customer It's all shiny again, I miss my scratches..