The version included in vim-core is 0.7 from 2006 while the latest is 0.9 from 6 months ago. See URL for details.
From the URL: "Updated versions will appear here, as the vim tarballs do not ship with updated runtime files. " So, it is up to the user to update the file. Otherwise, it is more difficult for devs to maintain the software (as it diverges more from upstream)
It could be argued that it is up to the packagers to update the file, and not the users. As a users it seems weird that installing vim with USE=python provides outdated files which should now be manually updated (or even emerged, which is weirder).
We've done updates for other vim runtime files, so I see no hard in updating this one as well. I'll put in in the next revbump.
Done! It is in app-editors/vim-core-7.2.359, coming soon to a tree near you!