Except that in season one it was Owen/Gwen, not really Jack/Gwen at all. Also Rhys/Gwen. I think that they set Jack/Ianto up from the first episode, but clearly it was even more behind the scenes in the first season, and they have chosen to develop both Ianto's character and the relationship. I remember on first viewing Cyberwoman assuming that all the rage between them was due to them shagging. Otherwise a lot of it was way over the top. Plus of course the kiss in that episode. Then the non verbal stuff in Countrycide.

I also remember on first viewing Capt Jack Harkness that I just thought that Jack/Ianto were casual. I don't think they would do that episode now without some kind of angst or repercussion. Even then I thought it was a little cheeky of him, but wondered if something changed after, as they did seem more properly together in End of Days.