Jean-Baptiste Queru, a Technical Lead developer on the Android Open Source Project, took to Google+ to share some of his insight on the manner in which Android updates are delivered. He also commented on which companies can be expected to deliver their updates first.
Sony recently released the update bringing the Tablet S from Honeycomb to Ice Cream Sandwich. This came five months after the release of the Ice Cream Sandwich source code into the AOSP. Queru had this to say on the matter. "This is actually a very reasonable time, since under the hood Ice Cream Sandwich is quite different from Honeycomb (and upgrades from Gingerbread are likely to take longer as those differences are huge)."
Queru also said that Sony has contributed to the Android Open Source Project far more than other device manufacturers. This means they had less changes to make before sending out the update to the Tablet S. Even with this advantage, the Asus Transformer Prime actually beat Sony to the punch. It received it's Ice Cream Sandwich update first most likely as a result of more resources being set aside to get it updated first.
Queru also mentioned his displeasure at the fact that carriers played a large role in holding back the update process for many devices. He was especially unhappy that several stock Google Experience devices have yet to be updated to the latest version of ICS. He was, however, happy that Google had recently gotten back into selling devices directly to customers and hopes to see the project expanded to other countries.