I am going to bet that Apple is going to do two updates. The obvious reason you alluded to earlier in that at some point the C2D will simply be unavailable. Being cautious about upgrades is usually wise, but I think that the gap from October 2008 through October 2010 was an isolated incident based on the gpu issue and working on the entirely due design.
Over the course of 4 months, the role of the Macbook Air and the 13" Macbook Pro have completely swapped. Before October, potential customers had to have a very compelling reason to purchase the Macbook Air instead of the Macbook Pro. I think now your average consumer really has to have a compelling reason to buy the Macbook Pro over the Macbook Air.
I think Apple really wants to make the Air their new mainstream notebook and will do everything to keep it updated.