I think you hit the nail on the head agerhart.
With 100 pages of good, useful content there will be many more keyword combinations, keyword phrases, terms you never thought of, etc. than in 10 pages of quality content.
I have a site I just put up a couple months ago. I was debating on whether to make it a simple 10 page site or make it a big complex monster. I chose the monster because there was a lot of content I wanted to write for that site. It is already paying off because every new page I put up can target some different keywords and phrases. Looking through my logs I am seeing many new ideas for pages based on what people are searching for as well.
I do have some small sites with only a handful of pages that do well but I usually go with the more is better theory assuming there is enough good content to fill a lot of pages.