I don't know ddraw very well; is there a better heuristic that occurs to you?
It's mostly just a consequence of the origins of ddraw; at least initially this was mostly just used as a replacement for the DOS model of applications writing directly to the framebuffer. Flip() exists, but isn't necessarily used a lot by early ddraw applications.
If it's just a matter of "some applications are going to blit multiple sub-rects to the front buffer", I'm inclined to commit this anyway, perhaps with an added code comment to that effect, on the grounds that a heuristic that works sometimes and fails other times is still better than none at all. I welcome disagreement on that though.
Yeah, as I said, I'm not necessarily opposed to this patch. I'd argue for tweaking the language a bit, perhaps "frontbuffer updates per second", or simply "updates per second" instead of "fps", but perhaps that's just splitting hairs.