Obviously they don't because they wrote it. However, /I/ consider it to be poor writing. Because I don't think leaving whether Jack and Ianto are in a relationship or if they're casually shagging or if Ianto is in love and Jack's taking advantage of that ambiguous does anything to help deepen the story or make it more complex or interject a level of tension to the show. During the show, we are never given a moment to make us question our own perception of Jack/Ianto, and that is the key point, I feel.

The show seems to be saying take whatever perception of Jack and Ianto you can scrounge up and it's all equally valid. Which is ridiculous. This is a relationship between 2 main protagonists and the state of the relationship says a hell of a lot about both of their characters. It says things which shouldn't be ambiguous because, like tencrush says, they are very central to what kind of man Jack is, things the audience needs to know in order to evaluate him.

And I do not think the purpose of television is to create fanfic opportunities so any argument about how this is great for fandom is irrelevant for me. Fandom is side effect of television not the other way around.