See, I don't think that writer would be at all off base calling Jack/Gwen an unrequited love story. Although, I'd probably describe it more like mutual unfulfilled crushing. That wouldn't sound as romantic to a writer, though.
It's not like that interp takes anything away from Jack/Ianto, either.
There's more than enough evidence that Jack and Gwen had feelings for each other, but it's obvious than neither was ever in a position to act on the feelings. Both emotionally, and due to previous experiences/committments.
I still love my ex, who now has a wife and three year old, and he loves me right back. That doesn't mean either of us wants to get back together. It just means that loving someone doesn't always go away completely, even when you've moved on in life.
Jack and Gwen can both legitimately love Ianto and Rhys respectively, without the fact that they were attracted to each other having any bearing.
I still get the impression watching Something Borrowed that we were meant to understand that they were both letting go of the attraction. The rest of the season even bore out that impression in their interactions. It was that point in a friendship-that-could-have-been-more where you decide not to pursue it for whatever reason, and start letting the feelings you have morph into something else. In this case, a more familial-style affection.

So, yeah. semi-OT to tencrush's point, but it's how I saw the whole Ianto/Jack/Gwen/Rhys love-square thingy resolving over the course of the season. I think they did intend to be ambiguous to a certain extent, but it resolved a little too neatly by the end to have been completely accidental.

I think the writers had to deal with the fact that in the first season their originally intended main ship got hijacked, and sent careening off in another direction. I don't think they did that bad of a job, either. I still maintain that the major issue is more to do with the akward romantic chemistry between Eve and John than the actual writing.