Hello, John. I'll try to answer your question. Actually, the opposite (without the а) can seem condescending in Russian. I'm from Uzbekistan and in uzbek too, it's like a necessity to use it to mean that "I told you my name, now it's your turn to tell yours". For example, -Ты был в Париже? (Have you been to Paris?) -Нет, а ты? (No, and you?) To tell the truth, I find it a little difficult to explain. I'd love native speakers to help out.
This is just a feeling based simply on the fact of the different treatment of "and" = "a" in the two languages - that without the "a", the Russian sounds more commanding, as if the speaker were demanding to know the person's name, and thus setting himself/herself in a high social status, which gives the authority to demand names (like a policeman or a government agent or a prince/princess or King/Queen. Just a hunch (notion), though.
Whether it's condescending or not depends on the context and tone of voice. I often hear it used in a way it conveys the eagerness of the person to learn about your experience, a positive interest and care. In Polish the construction is exactly the same with "а ты?" which equals "what about you?".
Just a thought, but wouldn't it make more sense to say "я Вера, а как тебя зовут?" Instead of "я Вера, а тебя как зовут?". I just don't understand why it is on that order, because I always learned "what is your name?" As "Как тебя зовут". If someone could enlighten me that would be wonderful.