Sorry about the multi quoting but I just realized this and I have to get this point across. As an IOS developer I have always been running Beta IOS software whenever it is available.
If Apple had to wait for carrier approval, then Apple constant beta system would not work. It hasn't passed through their certification yet. I am pretty sure the time release windows between betas are usually so tight (3-4 weeks), I dont see any of it going through carrier certification feasibly.
The day IOS 6 was beta 1 was release I was running it on my 4s. Right now I have IOS 7 on my iPhone 5.
IOS 6 had 6 updates all within 5 weeks of each other, with one of them only being 2 weeks between release.
Everything I have heard about Verizon would state if they had any recertification requirement, this would not even be the case.
Does Google or any of the OEMs release beta software so developers can run on their phones before the release time? My understanding that this is not the case.
In a weird way this system is more closed than Androids usual openness. And from my understanding, the platform developer kit given to OEMs focus on new phones not updating old ones.
So this is where Google may have some blame also.
Also think about cyanogenmod, they aren't looking at carrier certification. In fact, most of cyanogenmod issues involve items outside of problems the carrier. When you think about the other custom roms out there, it is the same thing. From what I recall on XDA, usually issues happen with sound, bluetooth, and other items, not a loss of wireless capability.
Now in learning about how Google operates I found out this great article on Android Central.
Why you'll never have the latest version of Android | Android Central
One other link, Sony made a blog post about the whole process after ICS was released. Explaining all the sets it has to go through also.
Ice Cream Sandwich