Pay them no mind. Some people have themes but out of all of the weddings I've been to or been in in my life, I've only ever been to 1 themed. It was 50s themed and it was cute but a theme is in no way necessary.
If you do end up choosing a theme, less is more. Don't overdo it or it becomes like a child's bday party.
The theme is "wedding". That's what I always tell people!
No but instead of a theme what do you want vibe to be? Fun? Elegant? Classy? Formal? I think vendors want to know more about how you want your guests to feel. Our goal is for fun and informal - we aren't doing a lot of traditional things and we are emphasizing the photo booth and dancing parts of our reception.
I haven't chose one and I won't. I get married on 6/17/17. I just choose my colors and from there on I have an idea of how I want to decorate which it will be with rustic stuff. So no I don't think you need to have a theme at all.
You don't have to have a theme, but it helps to have "buzzwords" or something that describes the style or feeling you want. For example I want my wedding to feel "rustic" and "romantic" so I choose decorations and elements according to that.