The general practice has been to give the devs a preview of the new iOS so they have time to update their apps for the release of the new iOS. If, as we all assume, the new iOS significantly re-writes how the home screen and notifications operate, then every app will be impacted in a fundamental way.
So, if we're not seeing iOS5 for the first time until June, then the odds we see a new iPhone are zero. They're not going to release an iPhone 5 with iOS4, and they're not going to unveil the iPhone 5 two or three months before its release.
It's coming in September at the former iPod event. Apple has smartly decided that it makes more sense to push new iPhones in the fall, when they make better Christmas gifts (because they are perceived as new rather than six months old, particularly if supply is still constrained), than iPads, which are to most people just too expensive to peddle as Christmas gifts. They needed to supplement the fact that fewer people are buying iPods, which means fewer people are interested in using them as stocking stuffers.
