I know this question has been asked before on Stack Overflow, but what I have not been able to find in the posts I've read are concrete references as to WHY one is better than the other (something I can take to my boss).

So I'm working on an MVC 3 application that is basically a rewrite of the existing production application (web forms) using MVC. The current site uses a URL rewriter to rewrite "friendly" urls with HTML extensions to their ASPX counterpart.

i.e. http://www.site.com/products/18554-widget.html gets rewritten to http://www.site.com/products.aspx?id=18554

We're moving away from this with the MVC site, but the powers that be still want the HTML extension on the URLs. As a developer, that just feels wrong on an MVC site. I've written a quick and dirty HttpModule that will perform a 301 redirect from the .html URL to the same URL without the .html extension and it works fine, but I need to convince management that removing the .html extension is not going to hurt SEO. I'd prefer to have this sort of friendly URL:

http://www.site.com/products/18554-widget

Can anyone provide information to back up my position or am I actually trying to do something that WOULD hurt SEO, in which case can you provide references on that?