When I was a kid, "delete" meant you were going to get rid of something... as in it would be gone after that. Google changes this definition. If you configured Gmail on your iPhone using Exchange with push support, the delete paradigm breaks down and instead your messages are "archived".
The official Google complaint thread: http://www.google.com/support/forum/p/Google+Mobile/thread?tid=0388614a7d4ba43d&hl=en&fid=0388614a7d4ba43d00047456d9a99bf0&hltp=2
The SupersUser thread: http://superuser.com/questions/196773/gmail-in-iphone-how-to-delete-on-swipe