I wasn't certain about the changed font size until I realized that the FTM Forums list was taking up less space on my screen. I don't know what Apple did, but the smaller sized font is remarkably clear.
I see the same thing. I hadn't realized it until you mentioned it. Maybe this is where the retina display comes into its own...
"sub-pixel kerning". Available only on an Apple display. (retina or otherwise, retina of course being better)
You'll notice things get blockier when viewing fine text on a non-apple display
of the same resolution.