I don't think its the 1 - 8 day rollouts that crawl up most peoples rear about Android updates. I rarely see people bitching that they had to wait a whole day and a half for 4.2.2 or something. Its the 4 - 7 month waits on other phones that annoy people. If other devices rolled out on the update speed that Nexus devices do, noone would give a crap. It would be a non issue, its more than fast enough.
Because they aren't going through both the carriers 'hold and check' process nor the OEM's 'Skin and check' process if its an unlocked Nexus phone. The carrier has no interaction with my Galaxy Nexus, neither does Samsung so theres no hold time while the carrier 'tests' shit. It just comes to my phone off of the Google servers. This is allowed apparently by the carrier if its unlocked, but not if the carrier is on the hook for customer support calls and whatnot (I.E. if the carrier is the point of purchase).
Its possible that some carriers will allow Google to bypass the testing, and some won't. But we need to look no further than the Galaxy Nexus on Verizon which is just now getting 4.2.2 compared to my Galaxy Nexus that got 4.2.2 like a day after it launched for proof.
Of course it doesn't, its probably just the carriers bullshitting. But thats the carrier, not the OEM apparently, and not Googles release of the code either.
I'm not sure I understand which part you don't agree with. The article is not implying that the OEM's don't add ANY time to the process, they are saying that the vast majority of the time added to the process is on the carriers end, NOT the OEM.
In other words, it may only take HTC a month to get a 4.2.2 update out, but once it hits the carriers, it sits for 3+ months in testing... Then Sprint rolls it out to their version, a month later we see Verizon push it out to their version, and perhaps AT&T never pushes it to theirs if they don't consider it a priority. I don't think the purpose of the article is to argue that an OEM's custom software doesn't play a part. It absolutely does, it just appears that, were it not for carriers, the updates would be twice as fast.