It depends on previous context. Myself and another career programmer couldn't figure out how to print a wikimedia image on my uncle's Surface RT. (We tried several different apps and looked for context menus in each one to provide a print option.) As far as we could tell, it couldn't be done without dropping to the desktop. My computer-illiterate uncle showed us that you can just pick print from the devices menu in the charms. (Apparently, the Charms is a hybrid system menu and app context menu.)
I didn't have any context for how Win8 works. He did. Then again, I don't know how long it took him to figure it out and whether we would have figured it out eventually.
Despite my bad experience, I'd rather see radical changes in UI instead of sticking with what "works". It only works because we're used to it. Win8 might not be a step in the right direction, but it's might lead to improvements.
"Make a completely foolproof product and only a fool will use it".
The whole point of a context-sensitive menu is that it changes depending on your context. I think they're usually for advanced users -- often the right click menu just duplicates commands from the global menu but it's a faster access method. The Win8 case requires it for all users.
Of course if the context is the same, then the menu should be the same. (Maybe that was your point?)