1st gen iPhone battery life issues: it's the apps?

I've had my original iPhone for over a year now, and I've had a pretty stable use pattern. I charge the phone often (every time I'm in a car (daily) and every other night attached to my computer) and rarely see the battery dip below maximum. For usage, I typcially use it for about 15 minutes of internet stuff in the morning, I'll use it for about 10 minutes or so around lunch, and I'll often go out for 60-90 minutes of daily exercise time using it as a music player. I probably make an average of only 3-5 calls on it a week, so it's mostly an internet device to me, acting in place of a laptop whenever I'm outside of my house.

In the week since the launch of the 2.0 OS, I've loaded my iPhone up with about a dozen apps, but mostly I've just tested them out or played with them for five minutes and haven't launched them a second time. The one app I surprisingly use (surprising because I'm not normally into games and not into cards/gambling at all) is the Texas Hold 'em game. I've probably played it an hour a day since I got the iPhone 2.0 OS.

What I've noticed so far is that if I play a few hands in the game, then hit the sleep button at the top to throw the phone in my pocket or put it on a table to be ignored, when I come back my battery will be down to a half or less. It happened the other night when I played the game before bed. I woke up to a nearly dead iPhone on my nightstand.

It's weird because I've never "exited" or "quit" iPhone's native apps before and I've never had battery life issues. I often just hit the sleep button when I'm reading email or in the camera app, and the battery will be fine hours later. Yesterday I noticed I played some poker, hit the sleep button, went away for one hour, and my battery was half drained.

I know it's a pain that Apple screens all the apps and I bet 3G and GPS are power drains on the new iPhone, but I have a feeling even the well-vetted apps are causing a lot of power consumption that wasn't happening in the past.

I'll concede this is just a hunch and I may be wrong, but after a year of a constantly full battery under mild use, the only changes I've made in the past week were using one new app, and my battery is now getting drained much faster.