Now, this may be a slightly radical view, but Star Trek is just a show. It is easier (and much better on one's budget) to have humanoid characters. It takes far less work, especially for a weekly show, to put people in relatively simple makeup. The black guy in ears, he's a Vulcan. You all know that. The girl with the wrinkly nose, she's a Bajoran.

When you see Leonard Nimoy in those ears with blue shirt on, do you think "Boy, why would Vulcans be so tall?" No, you wouldn't. You would think, "Hey Spock, do that neck thing again." There is a healthy thing in entertainment called:

Suspension of Disbelief

Who cares if Tuvok is a black actor. He is a Vulcan, trapped on Voyager. It's a story. Now when you think too hard, and try to extract too much meaning out of a show that wasn't meant to be read that deeply, then you are stepping out of that suspension. Voyager has a lot to live up to in the television category, and perhaps it is their fault for not holding the audience. Lots of other Sci-Fi shows use humanoids as characters. It helps the watcher to identify with them. I think that Tuvok being black is a good thing. It gives the show a bit of diversity for plot purposes.

So sit back and watch the show. Ask questions to yourself later. Follow the story line, and don't look at things that are not meant to be picked on. So not every show in prime time is extremely meticulous. Sit back, and be entertained. Save your level of circumspection for your own life.