The images seem to be over-accentuating the bend. You can see from http://www.htc.com/uploadedImages/Common/Shared_Image/Galler... , if you tilt your head a bit, most of the "bend" is just making the phone thinner. The front only sticks out ~4mm from the rest of the phone.
On my G1 it also protects the menu button (which also unlocks the phone from locked mode) from being pressed accidentally.
While you can configure an unlock touch gesture, I haven't bothered yet because I don't find that the menu button is being pressed accidentally in my pocket.
Well, it also helps with hand contour. And it makes it easy to identify the phone's orientation by touch.
And it encourages you to put the phone in your pocket the right way around... If you read the G1 user manual (yeah, yeah, I know), there is a curious passage advising you to keep the back of the phone 1.5 cm from the body.