I think you under estimate the value of the patent portfolio.
Apple and Microsoft desperately want to stop Android/Google because they see the danger. The acquisition of Motorola Mobility allows for the continued growth of Android and allows for Google's extremely successful and profitable strategy to continue unhampered into the future.
I am sure things will change a bit at Motorola over time, but I think Google would just be happy to have the patent portfolio and have a moderately profitable subsidiary in Motorola Mobility or even strip the patent portfolio and sell what's left of Motorola.
What some are forgetting is that because of it's meteoric growth, Android has fallen under increasing attacks. Lawsuits from Microsoft and Apple were a big problem for companies making Android handsets, and to increase profits Motorola was considering suing other Android phone manufacturers for licensing fees. These things were all likely to cause a slowdown in the proliferation of Android. Google has stepped up to the plate, and IMHO made a very smart move to protect itself and it's partners and done a great service to consumers by helping to allow growth and innovation to occur instead of the stagnation that would be caused by Apple and Microsoft's drain on the smartphone sector by continued lawsuits looking for draconian licensing fees and/or injunctions prohibiting sales of their competitor's products.