Humph!
I guess I haven't been paying too much attention, but I did go back to some updates that I did right at the RR roll-out time (back in Feb, 2004) and the times there sure seem like UTC to me. Of course that is 3 1/2 years ago and my memory may be fading, but our (wife & I) schedule during that period (we were in New Mexico) would indicate that I would not be up very late at night because of a need to be up at the crack of dawn. Some of those entries show some pretty late times, after 11 PM, if that was CST then on MST it would have been way after 10 PM, seems pretty unlikely to me.
In any case, I like it being on UTC, makes it the same for everybody when you reference something when talking about it to someone else in another time zone.