Thought I'd share this comment, since I believe this is the case. I am on a new MBP with HD Intel 4000 and I get the a strong blur on scroll. Doesn't matter if it's Safari or Activity Monitor. However, on iMac with Radeon 6970 the blur is much less noticeable.
"I've seen this type of effect on a number of systems and hardware. I think what the software does is create a lower resolution image of the page and uses tat to display when scrolling. This lower resolution image takes less calculation to show the movement of the scroll or zoom, and possibly allows free CPU timeto calculate and pre render what is about to appear in the scroll. When the movement is stopped, it'll then do a complete screen redraw at full resolution.
This type of procedure probably comes from mobile type devices where CPU resource can be limited and a balance struck between smoothness and image quality."
Also, Apple made a statement about this: