It's about how the vocal sits in the entire mix. It's a choice and it can be well or poorly done, but in general it's independent of the vocalist's singing or voice abilities. Do a web search for "reverb on vocals" and you'll see how large a topic this is. And yes, sometimes an appropriate choice would be to not use reverb (echo, delays, ambiance, etc.), but it really depends on the song and the arrangement.
Reverb
As my system slowly works itself up the food-chain, I can clearly hear more reverb in recordings - particularly with vocalists. Why is it added with singers who have great voices? With studio recordings, the room acoustics should be fine. For that matter, they might even be in a booth. (Reverb makes sense in recordings with not so great voices.)