I have owned an iBook G4 (don't blow up just yet) and the plastic MacBook. I can tell you that it's almost the same size. The MBA should suit your needs perfectly, because no "pro" would use laptop anyways. "pros" use Mac Pro (see how the the word pro comes in?). If you are really a "pro", you won't be asking for more portability. You would be asking for a FW 400 port on the MB since the graphics have been updated.
If you really want to *wish* for a 12" MBP, be my guest. But I doubt it will happen. One, graphics. Graphics technology is much more advanced and the gpus run at higher temperatures than before due to much faster speeds. Two, cpus. *read above.* and three, what kind of pro would uses a laptop for their professional work? They would use Mac Pros with 30" ACD. And maybe have a lightweight laptop with good graphics for on-the-go, such as the MBP or MB or even the MBA. Why would you need 4GB? That's another story...
The MBA is supposed to be a WIRELESS machine. That's why it has only three ports. Audio for listening to music, USB for flash drives or the super drive and display port (the newer ones) for giving presentations. Apple thought it all out. You don't need more for a ultra portable machine.
Having everything high tech into one product will distract people's attention to buy that one machine that has it all. That's what previous people meant by cannibalizing the lineup. There should be a balance, so MB for average users, MBA for ultra portability light weight usage, MBP for high end users with two graphic cards. iMac for home desktop, Mac Mini for average users, Mac Pro for heavy duty usage and tons of raw processing power.