Well carriers do play a hand in updates -- even on iOS. They have to ensure the software works with their network. They aren't just going to have phone manufacturers push whatever without ensuring the network experience doesn't get hit.
If there was an issue on a specific carrier that had to be addressed (either in the update or server-side) I could then very well see it being delayed for QoS (Quality of Service) reasons... but a carrier isn't just going to block it to be like "Ha you must wait longer!" is mainly my point
.
Under normal circumstances once the OTA is released we should all get it within ~1 week or so.