I recently converted a few e-commerce websites from OS Commerce to my own e-commerce software, and I've seen tremendous changes at MSN as a result. The main difference between OS Commerce and my software is that my software sets up a directory-like structure for the products. Let's say 30 different category pages in shtml, and 80 product pages in shtml. Just like that the websites went from nobodies to #1 at MSN.
Part of that might be the way OS Commerce uses session ids in their linking; I don't know.
I had a similar experience when I converted an auction website from Cold Fusion to SHTML with PERL as the dynamic language. The category pages are all SHTML now, and the items are displayed with a CGI script. Now the website has 65 or so different category pages, where it only had one CF script for displaying categories previously. It's #1 at MSN for almost any relevant search term you can think of.
So, I'm fairly convinced that the number of differently named files has an effect at MSN. And like I said, the relevancy of those pages probably matters--I doubt that you'd get a high ranking at MSN by making 100 pages about anything.