Could be you don't realize how much better it could be because you don't have one. People are happy with TV speakers until they hear a good sound bar. People are happy with a good sound bar until they hear a good HTiB. Those folks are happy with the sound until they hear good little pair of bookshelf speakers with a starter sub. etc etc.
Not at all. I am the only one of my friends and neighbors with an HT system who doesn't use a center. I have heard their systems, and most are more ambitious than mine. Two use large projection screens with a third instance of their L/R speakers. From the perspectives of center imaging and voice intelligibility I've never heard an advantage over my system, though as I said I use a 70" LCD display, not a 130"+ screen. With a projection system I might use a third L/R speaker as a center. A few friends who have auditioned my system have asked where the center speaker is, and are surprised when I say there isn't one. Every person who figured out I use only L/R speakers have been surprised at how well the stereo image works, and mentioned that they assumed "an expert like me" would use a center, a sub, and at least two surrounds. Maybe a sub or two one of these days, but for the HT content we tend to watch even subs would be a waste.
(As a somewhat unrelated aside, I do have a gripe with many people I know and meet with their assumption of expertise based on big expenditures. While my HT is modest, I have spent a considerable sum to most people on the music system, and my friends assume because I spent new BMW money on it that I must be an expert. The same goes for cars, boats, guns, etc. Buying something expensive does not confer expertise, only proof of the means to acquire. Why do so many make assumptions? I think I do know more than average about audio systems, but simply owning $30K worth of speakers does not make anyone an expert.)