"the Kindle and the iPad being the exception because of their close relationships with the content production sectors. And without content, neither Microsoft nor Google have much of a story. Google is relying on the increasingly bare public internet for "stuff", of which nothing is exclusive to Google. "
You seem to be missing the Google Play store, which now sells books, TV shows, Movies, Magazines, etc (just like Amazon and Apple). You can also use the kindle app (amongst others) on an Android tablet to view Kindle purchases.
IMHO the main thing that's missing from Android tablets is apps... and Google releasing a cheap but good (as opposed to the many cheap and rubbish Android tablets on the market) will kick start tablet app developers, and make people wonder why they're paying triple the money for an Apple Ipad that essentially doesn't do much more than the Nexus 7.