I don't buy that. Flash can do everything Parallels can, and - like the article said - inside Parallels flash is running faster!
The issue here (with the 10.1 hardware acceleration) is that it requires updated video drivers, and Apple controls those drivers on OS X, and Apple hates Flash. Maybe they will eventually add support, but why would they hurry if they don't like it in the first place?
Parallels does not have updated video drivers from Apple, why should flash need them to match what parallels does now? Whatever Parallels installs or does to handle dismay updates, Flash plugin could do.
Parallels doesn't run in a browser.