If you are good cook, and know the characteristics of the cut of meat you are using, you can turn out incredible food on either a gas or charcoal grill. Anyone that says otherwise simply doesn't know how to cook on one or the other properly.
FTR, I have both. I prefer my gas grill on weeknights after work, but enjoy cooking on the weber kettle as well. I also have a WSM, and use it to smoke all the time. Smoked trout today. Having said that, a weber kettle is a very capable smoker if you know how to use it.
You can also smoke on a gas grill. Simply place wood chips in foil, poke done holes in it, and throw it over the burner.