Well, some believe that having only 2 rings provides smoother shifting and that you can get pretty much the same gear ratios with a compact that has a 27t rear. Personally, I have always had a triple; when I was about to get a compact double on my Trek 5200, we moved to a street with a 10% grade hill. I kept the triple.
DH went from a regular double to a compact, when they first came out. It never shifted right and he spent a lot of time working on it. I think he actually bought a different one and had that for 2 years. When we bought the bikes we have now, he got a triple.
The "thing" about having a double comes from racing, where having a triple is, well, not for racers. But since most of us are not racing, as long as you have a finely tuned triple, who cares? I have never had any trouble with my Ultegra triple. I *did* have lots of issues with my first road bike, which had crappy components. In fact, I never used the big ring, since I could push the lever to get it into that gear.