Yes. One extra year to test and release the update. Why would it take Sony any less time? And Samsung simply abandons a lot of phones. Galaxy R, Galaxy S Advance. Check how many updates they got. Sony uses an year wise policy, all phones released in year x would be upgraded to version y, so the testing would take longer.
Well yeah. It is clear that Samsung is doing a pretty good job at least with their flagship devices. There are no doubts about it. Sony and HTC needs to do better with upgrades. Hopefully with quad core devices becoming common today, things would get better in the future.