I had four on-campus interviews last year. Three of those four asked my basic startup costs. None of them made an offer.
I've been told that dept chairs ask for this info upfront so they can start the ball rolling early on getting those startups confirmed by the higher-ups in administration. If they have an idea of what their candidates need on average, they can start to request those funds from the Deans and get signatures even before the final candidate is approached with an offer. So they are using you as one of several datapoints to determine that average.
I think it's also a way of very roughly filtering the candidates - if you ask for something completely out of the ballpark of what they are able to offer, they will use that as a datapoint against you. That said, you are unlikely to be seriously "dinged" for this, because schools will already have a very rough, basic idea of startup costs based on your CV and the kind of research you do. If you are an imager, and they don't have an imaging facility, you are unlikely to make it to the interview stage. So they will probably be okay with whatever you say (so long as it's within reason and you can back up why your research needs those funds). Even if you do propose too high, it probably won't put you out of the running automatically - I've heard of depts going looking for extra startup funding when they are absolutely in love with a candidate.
So, don't take it as any particular good or bad sign, and don't worry too much about what you propose for your startup - that will all get settled in negotiations.