Well frick...I had just typed out two long paragraphs in response to this, and then accidentally clicked back and lost it.
The show keeps going back and forth on events because it has to have narrative tension or there is no show. You already have one couple that has narrative tension, Lilly and Marhsall. You can't have a whole show of people in established, functional relationships or the show is over.
My basic point was that maybe I was missing something when I started watching the show (because I didn't have the first three seasons' worth of history to draw upon), but I don't think Robin and Barney have been being "pushed" since then. Maybe I was off on reading that though.
But in a show that tries to be so self-referential and tries so hard to make sure that minute details matter to the overall plot of the show, it sure as hell seems to do things solely for filler. They've built this huge vault of information that is crucial to the plot of the show, but then they go and fill half seasons with irrelevant shite. I can understand the "I don't really care about the plot or who the mother is, I just like the show because it's entertaining" argument, and I actually pretty much agree with that viewpoint. I just don't like how they finally let Barney grow up a bit (with his relationship to Nora) and finally let him meet the girl of his dreams, only to have that rug pulled out. Same thing with Robin and Kal Penn (although admittedly, that was always seeming to go nowhere). They're together, and it doesn't seem to feel right. Then they're not. Then they are. Going back and forth is one thing, but at some point it almost seems disingenuous...like they are just toying with the audience knowing they're just gonna pull the rug out from under them again (and again). Like I said, I can understand why that would upset/frustrate viewers. It's like they want to do things and set up certain things just so they can be like "HAHA, frick you." Perfect example is it wasn't but about 5 or so episodes ago that Ted was confessing his undying love for Robin. WTF?