There's a whole repository of unused system files that have been patched over -- just in case someday you decide you want to uninstall updates. And versions of system files so every application can have the exact set of libraries it expects.

They may have removed the burden of resolving dynamic linking issues from the user, but now the disk carries it. It's all a huge mess, it keeps growing, and I'm not sure how (or if) it can be fixed.

The iOS model (thinking phone / tablet methodology here) is to release the new OS libraries with as much backward compatibility as is practical, and let the app designers fix any lingering issues. Given the Windows market's dependence on obsolete applications, I don't think that would pan out.