Have you actually used office? It has change tracking, diff and merge and has done for over 10 years. The problem here is network locking which is totally different.
The change tracking in office is nothing at all like the "See Revision History" in Google Docs. The Google Docs one is miles better.
Regarding SkyDrive, you're talking rubbish. It's been there for literally years.
Right click a document in skydrive and select "Version history". You can review every version, restore earlier versions and open the changes up in Word if you have it installed and review there.
If you go "big" and use O365 you can review and accept, annotate all changes and commit to sharepoint for example from your desktop app.
You can even wire it into review workflows so that commits are staged and reviewed by an editor, people are notified etc. This is great for legal documents, contracts etc.
Google Docs doesn't get a look in.
It takes about 5 seconds to change which revision I'm looking at, in a 30-line document. And it doesn't actually show me which lines changed.
This is still useless.
I'm not getting a 5 second delay here. It's instant (~0.5 seconds).
You're right about the changes not being marked up, although it does do this on Office 365 so perhaps it's a market segregation thing.