Jesse,
One of the things that I like to see from my provider is going the extra mile. For example, my logo designer made a sketch of what I ask him for, then he also made two more sketches of what he thought was best. I eventually made some modifications from one of his creations. I appreciated his hard work and since then I've used him 3 more times to make other logos.
My experience with my web designer was the opposite. He made exactly what I ask for. I didn't like it and he had to make several revisions before it was accepted. I felt he was trying to cut corners and give me the quickest design so he could move on to the next customer. Since then, I've used 3 different web designers. Each of them had the same level of service which makes me never return.
I think the web designers do not make additional mockups because it is time consuming. But it's not so time consuming if they realize that without the mockups, they will have to make several revisions. Also, how much time goes into making several revisions and how much time is lost when you don't get repeat business.
I'd like to see web designers take the same approach as logo designers. When you quote the job, tell the customer that you will make 3 mockups. That would impress me.