I'd imagine the difference in CPU Usage differs from HTML and Flash content, and also what you're running it on.
If you're using the GPU, CPU, screen, HD more, then it'll use more battery in general. I wouldn't be able to say if there's a direct link between battery life and decrease in CPU usage - it seems a more case by case basis.
If you have a larger CPU, or less crappy Flash (e.g. well coded/minimal) then you'll see that it'll use less CPU i'd imagine.