I'm not sure which version of DotNetNuke included this magic, but if you create a page with tab name Sample Page, then you can simply access that page with portalAlias/SamplePage.aspx.
When I see this thing first time, I was impressed, and tried some more tab names with this. Next is to create a child tab of Sample Page called Child Page and tried and it doesn't work. I scratched my head for some time and tried /SamplePage/ChildPage.aspx and it worked.
I'm using dnn 5.x and it works nicely for almost all the pages.
Then I tried some more magic tabs and I come to know that there are some pages in dnn that are always available to all the portals and child portals regardless of they are created or not. For example, If you type portalAlias/login.aspx it will show a login window. If you try portalAlias/LogOff.aspx it will immediately logoff you!
It's nice to know this thing, because it will be useful when you are developing a new skin. If you forget to place login skin object and want to login or logoff, its easier to do that with this.
I assume this is a magic from dnn friendly url provider. I've come to know about this just before some time and thought it may be helpful to you also!