One of the reasons why Android updates tend to get held up at carriers is that the carriers don’t allow the updates to be released until they sign off on it. That’s why you see unlocked handsets getting OS updates before carrier locked devices. Microsoft has tried to avoid that for Windows 10, bypassing the need for carrier authorization. A representative for AT&T has confirmed that Microsoft can indeed push out Windows 10 updates without needing approval from the carrier.
The representative mentioned this in a response to a query on the official AT&T forums. The representative confirmed that AT&T won’t be holding up the update to certify it, and presumably that’s the case with other carriers as well, since Microsoft doesn’t want the updates to be held up.
Microsoft has made it clear from the get go that it views Windows 10 as a service and wants to stick to this strategy by ensuring regular updates that bring timely bug fixes and security updates aside from new features.
Windows Phone users would appreciate that these agreements eliminate the need to wait for carriers to first sign off on updates, they get the updates when Microsoft sends them out, resulting in a much better experience for everybody.
As far as firmware updates go carriers do need to approve the update first because all drivers for radios, etc first need to be tested and passed, this is an essential step to ensure that the firmware updates don’t have any issues before they’re sent out to end users.