Gratuitous screwing of customers aside, I'm trying to figure out what the benefit for Verizon is. Do they get a lot of customer support calls from people who don't know how to use the phone, and need time to train the call center staff? Or is it simply their reflexive control-freakery? Clearly they survive a lack of control from iOS.
Google has, in the past, pushed out updates to phones in ways that bypassed carrier certification and then broke things (e.g. in the early days of Market auto updates). Because people buy the phone from the carrier, if it breaks the carrier gets to pick up the pieces. This is especially true because whilst Apple has extensive on-the-street support infrastructure and everyone knows if you have a problem with an Apple product you take it to the Apple Store and they fix it, no questions asked, this is not true of other phone manufacturers. The carrier provides the (very expensive) in person support.
Verizon may simply not trust Google's QA process, or put another way, they institutionally don't trust OEM QA processes and to make an exception for that requires a very good reason beyond just "Google is cool".