While you make some valid points, you overlook others:
1. As soon as the new model comes out, the older models will drop in price. So even if you aren't getting the fastest and greatest, even if you're buying the lowest end MBP, you'll benefit from the price break.
2. MBPs are expensive computers. You're investing in something that you'll keep around for 3-4 years. I want to future-proof my computer as much as possible. Features like easily-swappable HD and fast graphics card will affect "the average user" 2+ years from now (pro'ly sooner) when everyone's downloading and streaming HD videos and OS X has all this new eye-candy that will require a fast graphics card.
3. There are other features than just a 10% increase in CPU power that we are hoping in the next MBP, including a magnetic latch, easily-access to HD and RAM, and better heat management. Certainly the average Joe will be able to benefit from these features, even if all you do is word process and surf the web.