Im going out on a limb and assuming the WWDC will include the iMac update. With Intel delays on certain mobile/portable ends, the guaranteed desktop Ivy Bridge release denotes the iMac will come before the Macbook release... in my opinion.
Plus a ML and iMac paired release would be a very elegant, sensible way to go about it. Even if it was ML paired with the MacBook lines, a new operating system "optimized" for the new iMac/MacBook would be a great selling point for prospective buyers. Keep in mind, the more features you pack on to a new product, regardless if they are upgradeable or not, increases the value proposition for any consumer, even though it may not technically result in a financial advantage.
Its all a psych game, and I think Apple will really try to wow the market, especially since there has been such public disappointment among recent releases. But thats a whole new issue, and I personally think consumers are getting unreasonably greedy with their expectations