The difference is you don't type in www.somedirtypornsite.com into the google.com search box. You type it into the location bar. This is the first time a browser is auto searching from the location bar.
Many people use google's main site as a location bar. I've seen this quite often, even among people working in science and holding a PhD. It's not only my granny.
After writing this comment I saw another comment http://news.ycombinator.com/item?id=294070 of a person that says he does this. So it must be quite common.