I am not surprised
I have two xperias in the household and the next raft of upgrades will be Xperias too.
The latest and greatest software is not everything. In fact, I would rather have _NOT_ the latest and greatest, but some level of quality assurance on whatever is shipped. The amount of bugs I have encountered on my "fleet" is inexistent compared to some of what I have observed on "leading edge" Samsungs (and iDevices for that matter). Hardware is similarly excellent. Compared to HTC or RIM it is a "no contest". You take one, you take the other and you walk out of the shop with an Xperia in hand.
My only gripe with the Xperias so far has been that they are very picky on what they connect/charge from.
So Sony overtaking the other also-runs is not surprising. Just get an Xperia for a few months and you will understand why (as well as why it was one of the very few Androids to hit a 90%+ el-reg review rating). I hope they keep up with this level of commitment to quality in the future.