I'm in two minds... No, they do not create a 5.1/7.1 like affect, but they do provide a very broad sound stage. As many sound bars have separate subwoofers, they can offer A LOT more bass, which is severely lacking in modern TV's. Personally, I'd have a listen to one, and if you think it'll be better than your current TV speakers, do give it some serious consideration.
Yamaha has options, but so do all the other players, Panasonic to LG.
Of course, a set of efficient bookshelf speakers + a class D compact amp like you'd find from NuForce can provide a decent solution. Don't ignore that option, especially if you enjoy a little music from time to time.