Why VS does not have support for undo/redo files?
If that features does what I'm thinking it does, it's basically a function of your source control system, and isn't something that should be handled by visual studio. On the other hand, VS does keep a complete history of every change you made since you opened Visual studio, and you can undo an redo changes for the entire day, or even week if you leave VS open long enough.
It would reproduce the functionality of a revision control system (such as Subversion or CVS), but without some of the benefits of those systems (such as tags and branches). That's probably why it isn't there (or in many IDEs). Many people seem to be discouraged from using revision control for small projects, but it's worth the initial setup and can be shared among many projects.