Page Routing on IIS6 v. IIS7

We have a custom CMS that uses page routing. Currently, the system uses clean URLs that end in "/". Supposedly, this is fine for IIS7. But our understanding is that in order for page routing to work on IIS6 all URLs must end in ".aspx".

However, our CMS and it's page routing works on IIS6 even though all URLs end in "/" and none end in ".aspx". We had planned on updating our CMS to print URLs ending in either the "/" or ".aspx" depending on IIS version, but it seems that may not be necessary. We have tested this on two domains on servers on IIS6 (win27 and win33) and page routing is functioning with only "/".

While I certainly won't complain if we don't have to code for ".aspx" depending on IIS version, I am quite curious as to WHY this is working on IIS6.

Anyone have any thoughts? Thanks!
I'm not the programmer so, keep that in mind with this answer. :)

I'm told we are using the C part of MVC for page routing. I assume that means, yes, we are using MVC.
If it is using MVC does this mean it would work on IIS6? Or would it only work on certain IIS6 servers that have received some update that allows this to work? I'm just a bit hesitant to have this deployed to all existing clients on IIS6 until I understand a bit better why it seems to be working. :)