Apparantly Samsung is not the only one doing ROM updates and Sony Ericsson being a beginner in Windows Mobile with Xperia, it's good to see that they offer updates too. Probably they don't wanna be bashed like HTC for poor support or offering no updates to older devices.
The new updates possibly fixes the frequent bluetooth dis-connection along with some minor bug fix and improvements. Also to note the new carrier selection at the initial boot of Xperia and a Google search bar pointing Opera mobile right from your Today screen.
Some people mention that they couldn't download from official site and we've got mirros for you to
download.
While these companies offer updates to Windows Mobile 6.1 itself probably after bug fixing, the question of Windows Mobile 6.5 updates after official launch, to their existing line-up of devices still remains a mystery.