Between undergrad and grad school I worked for a Fortune 500 company in hr as a staffing and development manager. I interviewed a lot of managers and I would say the question about benefits came up in about 1 in 10 interviews, maybe slightly less often, so it's not actually an uncommon question. However, as someone with medical concerns, I am sensitive to this question, and my decision to hire or to move forward on a candidate was not influenced by someone asking about benefits (I look somewhat unfavorably about questions on compensation in general). As someone previously suggested, I would wait until after you've moved forward in the interview process before asking about benefits. I know at least with my company we did not expect you to make a decision immediately after we informed you we would like to make a job offer. Depending on the position, they should give you at least 24 hours. We typically gave up to a week.
If it's a bigger company, the company and hr does not typically handle all benefits directly, they contract out certain portions (for example health insurance, long-term disability, group legal, and 401k). So when I made a job offer and someone asked specifically about benefits I could give them the number to our benefits administrator (we took care of pension in house, along with short-term disability, stock options, mortgage and adoption benefits, and college loans) or to the health insurance benefits administrator at the health insurance company. At no time do you actually have to give your name pre-hire to ask questions to find out about the insurance to inquire about the benefits. Also, most bigger companies make known their benefits if it's a particularly good package so you might do some googling to see if you can find out beforehand.
