Apple has switched to the 2.2 Gamma. Don't know when though, probably the 10.5 or 10.6 era.
I don't know if it is relevant but OSX uses a 1.8 Gamma whereas PC's (& TVs) use 2.2
i don't know. it's not libfreetype. fontsrv asks the OS X
graphics code to render each glyph into a box and then
concatenates the boxes to make the subfont.
all the text was noticeably lighter (more grey)
than in your screen shot when i put them side by side.
this is due to apple's algorithm for rendering glyphs.