I'm not surprised by Verizon wanting to maintain as much control as possible, even if the hardware did not originate with VZW.
I am puzzled at the difference in arrival time, of the security patch, within the same service provider.
I take it more as Motorola wants to make sure it didn't break anything.
In my experience, Motorola does OTAs in periods of push (available to certain IMEIs in batches) until it's available for everyone to pull down.