I agree, it's important for you to get an idea of what healthcare entails. Healthcare courses tend to have a high drop-out rate so I guess the admissions tutors want to see that you know what you're letting yourself in for so you don't turn round a few months into the course and say you don't like it, I've been told similar by a mentor at the hospital I did some shadowing at. Also, nursing is very competitive so it helps your application stand out.
Some unis are stricter than others on it, but I have heard of a few people who were accepted with no experience, but really for your own good you should try and get some. It's not so much the amount of hours you can put down but what you've taken from it.