When a TV doesn't have to scale (for instance if you set the 360 to output 1080p on a 1080p set), does it blur less? Or does scaling have absolutely nothing to do with how much a TV blurs in fast motion?

yes, scaling and/or de-interlacing can induce blurring and/or display latency, in addition to other post processing "features" a particular tv set may have.

when at all possible, display at the native resolution of the panel/tv with no post processing.

Scaling can both cause things to look blurrier or sharper, but it has nothing to do with blurring during fast motion, that's just the way LCDs are. But setting the 360 to 1080p is mostly just moving the scaling to the console as most content on the 360 is lower resolution, and whether that will look better or worse if any different at all depends only on how the 360's scaling compares to that of your TV.