When you do a View Source, you are not looking at the Source Code, but in fact, the Output. The Output (HTML/Javascript/etc) is rendered by your browser.
But to answer your question, all of the pages are technically .NET pages. However, most of these pages are simlply "wrappers" for the old ASP page. The .NET Page (ASPX) simply calls the ASP page and writes it out.
The category/game list is fully written in .NET (and which is why the sorting and whatnot is so easy).