the only way they would just release it on a Tuesday with out the typical press event was if the form factor were staying exactly the same and the Apple home page just said "iPhone: Still the best mobile internet device, communications device, and iPod. Now even faster and smarter with 3G and GPS." This would be a similar kind of update as the iMac and macbook (pro) speed bumps. Not an outright redesign, but a marked improvement in the internals.
If you look at the iMac, they had a press event for the unveil of the Aluminum form factor, and haven't had any since then. I think the iPhone will follow a similar trend. Even iPods only get press events if the form factor changes. Price changes and memory bumps (shuffle, touch for example) just get a homepage banner
If this were the case, I'd expect a release this week or the next, and the WWDC to be focused on the SDK, possible some OS X, maybe new notebook form factor or whatnot. which would be fine with me, I love the current form factor of the iPhone, and I want one asap lol
Otherwise, if the form factor changes, it won't be until WWDC that it is announced and middle of June for a release.