it's not accelerating the one thing that would make the card unecessary for the rest of us, that would be scaling and rendering to the screen. Rendering in flash is not done in overlay mode, so it's like you're drawing the image to the screen with the cpu, not the gpu. This is fine, if the cpu is unloaded (via the broadcom card). The scaling, since we're not using overlay, and thus the gpu at all, is also done by cpu. Again, if the cpu isn't loaded this can be done easily.
Though, all adobe would have to do is change the way it outputs video within flash so that it behaves like a normal media player for such content and we'd get performance similar to what native formats (non-flash) media receive. That being, we could play back hd content without an accelerator.