I don't think they'll muddy the waters with that at an iPhone / iOS launch event. MBP refreshes would either distract from the iPhone or be ignored, neither are something that Apple would want.
Refreshes have frequently gone out in the past without any sort of event and I'd guess that this would be the case this time.
the rumours this summer were pretty confident of not just a spec bump but a new air-like design for the next iteration of mbp. i'm sure it'll get it's own event.
