It is certainly *one* major reason. The other is freedom from carrier bloatware/spyware/unreasonable restrictions.
That said, I'm rather disappointed that they did not make some effort to return some control to the user: not only is the ability to edit app permissions lost, but once a google account is attached, it is impossible to add device-local contacts (i.e., only cloud contacts can be entered).
One must wonder whether Kondik getting a job at Samsung has altered his allegiances.. He did fight against providing anonymizing data in a patch submission for CM7 -- because it would "piss off" carriers/Google. Well isn't the point that the device should serve *us*? If such a move caused pushback, then it would certainly reveal how these companies actually regard us -- the buyers of their hardware, but to them mere slaves and acolytes.