Yeah, even though the W810i has been picked up by carriers recently, it has been out for a while in Eurpoe/Asia in its unlocked and unbranded version. With FCC regulations and time testing if a carrier firmware can be stable enough to use a given phone, North America is pretty much late in terms of cellular technology. Its replacement, the K550i, has alresdy been out. And the W610i is set for launch very soon. The K550i & W610i can be more related to people with the K750i & W800i. But the features are more with the W810i. The K550i/W610i just improves on what users felt what was left out from the W810i, like: A2DP stereo bluetooth, updated UI, and such. This has been how SE usually rolls out new handsets, they refresh what has been working for them and just add/improve a few more things on certain models.
But even though the W810i has already been replaced, it's still a great phone that has a lot of features packed in one small device. The K550i/W610i are for people who want an updated look and for what some feel certain features should have been included. The new UI alone is reason for some to get it, because the organizer is comprehensive enough for some people who don't need a smartphone but want a bunch of options for a certain thing.