Some extensions - for some reason - have the same greyed out uninstall button, as you mentioned here when starting VS2010.
However, at the bottom of the window there is also a small text for these extensions: "To remove this extension, you must use Windows" Add or Remove Programs. "
This is a bit strange, but I expect this to be due to the fact that some VS2010 extensions require additional installation behavior that cannot be cleared from the VS2010 extension manager.
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