History of full of software companies who thought they were too big to fall - and either Apple OR Adobe can fall into this trap. Working with both of them everyday all day, I would venture to guess Adobe would first. CS4 is better than previous releases (haven't read up much on CS5 yet) but it's nothing Earth-shattering that couldn't be replaced (as Quark learned). Granted it wouldn't be *easy* to do overnight, but if Adobe suddenly announced CS6 would be PC-only (which they won't do, because they do have shareholders to answer to and throwing away 25-30% of your revenue is ridiculous) there would be lots and lots of successors to the throne released before CS6 ever hit the street.
Apple learned a LOT from MS Office specifically I think - if you own the file format you own the market. As long as they can keep popular file formats Mac-compatible they're ok. That's the push behind this Flash deal. Adobe controls it and can take their ball and go home whenever they feel like it. If Apple pushes content creators toward neutral file formats, then they never run into a scenario where they get locked out of content ( which diminishes the appeal of their shiny, lust-worthy products).
Just my 2¢