This is most unfortunate for those who purchased through Steam. I was going to do the same but read on the forums that once purchased you had to buy all expansions also through Steam and so I decided not to do that as it meant I could not shop around for the best deal.
I'm pretty sure nothing is going to change with regards to this though as it is all down to contracts. Ideally SE should permit people to register a non-steam PC version but I bet Steam made sure that was forbidden in the contract.
