I'm tempted to read too far into the colors on the invite (especially after the 5c announcement), but I suspect that (like the 5s and 5c announcement) most of what's going to be announced has already been leaked.
Would you be upset if they were slowly fading MacBook Pros out and instead replacing them with the retina MacBook Pros? From a different perspective, what if they were trying to drive the cost down to produce the rMBPs? Biding their time.
I just hope they release new MacBook Pros.