As an additional follow up... on my f10 system .. i have 1814 unique binary packagenames installed... 185 are -devel subpackages.
The intersection between the 1815 packages I have installed and the 7173 available updates is 823.
775 out of 823 are updates to packages available at release time
48 out of 823 of those are packages not available at time of release.
74 out of 823 are updates to -devel packages
So taking this system as typical... and I'm always loath to actually do that. The thought of myself as a representative user of any technology is disturbing on many levels. But for the moment....assuming my system is typical...
I've got ~11.5% of available updates installed by package count (not by package size). 99.5% of my installed updates are true updates in the sense that that a version of the package was available at F10 release.
I probably go back and do the same sort of analysis on my F11 system tonight and do a delta rpm bandwidth savings analysis. To get a better sense of what really is typical I'll need to datamine mirror activity logs.