I doubt the new product will be a "something for everyone" product. With the exception of the new line of notebooks and desktops that came with the Intel chips, the new products announced in the past few years have catered to a specialized crowd, instead of the average guy looking for a computer or mp3 player. This can somewhat be seen with the iPhone and iPod Touch, a bit more with the Mac Mini and especially with the MacBook Air. Unless they introduce a powerful but scaled down sub-$1000 notebook or something similar for the budget-conscious consumer who needs more power than the Mini, the new products will something amazing for the niche that needs it, but won't appeal to everyone. Also, for those who say that Apple wouldn't create a product that doesn't function out of the box, the MBA is pretty useless without another machine. Same with the iPod. With the Back to My Mac feature of Leopard, I wouldn't be surprised if we see more thin client like products to encourage people to become a multi-Mac household and get a .Mac subscription.
I thought some sort of deposit was required for a pre-order, if not the whole cost up front. Although I know they won't have a problem moving the iPhone, not requiring anything from the consumer is kind of risky no matter what product you're selling. That being said, I still don't doubt a pre-order of the iPhone, with a ship date in June. It would affect sales numbers but the number of units sold wouldn't suffer as much. It would be nice if they came out this month, though. I didn't really want one when they first came out but I'm thinking about getting one now. I don't like to get products when they originally release, though, and I need it at the end of June, so this would give me a month to decide.
And while I'm somewhat skeptical about it being released before WWDC, mostly because I can't imagine what bigger news they might have, I also doubt they would go for a month without sales just so people couldn't return them when the new one came out. For people who really need a phone and just casually decided on an iPhone, if they aren't available they'll completely lose those customers. Apple has always released product updates without much warning. The MacBook Pro is constantly getting updated, and I'm sure other products, too, but I don't really follow them. Anytime you buy a Mac you should expect something new in a few months. I don't think there would have been as big an uproar about the iPhone if it was just an update, but it was an update along with a price drop.
As for getting the new iPhone if you take your old one in for problems, I think it's possible. When I first bought my iPod the person who sold it to me said not to get the engraving because if something happened and it needed to be replaced it would be replaced with whatever model was currently out there. The engraved one would be sent for repair, even if it was major. Also, I ended up with a MBP because I was having problems with my PB. This was after they stopped selling them, but refurbished ones were still available. The genius gave me the option to repair or replace, since there were other factors involved, but I don't think he had enough clout to get me a brand new machine if it wasn't their policy to replace them with what is current. And considering the iPhone stock is depleted, it would be a bad business move to hold on to some just for those people who happen to have technical issues with the phone right after the new one comes out.