I'm not sure why Adobe deleted the linked archive of deprecated features over time found here ( http://helpx.adobe.com/dreamweaver/kb/deprecated-features-dreamweaver. html ), the closest article they have left is here ( http://kb2.adobe.com/community/publishing/923/cpsid_92324.html ).
Regardless, ASP.NET support was deprecated back at CS4. If you added a number to CC this would be CS7. So we have been since 2008 with no support for ASP.NET. Classic ASP was technically supported, although there were many articles posted about the server behaviors being out of date, on both ASP and PHP sides, which caused Adobe to listen to the masses and discontinue legacy support for that if they were not going to be updated because I think we can all agree it would be better to remove something that could potentially open up security holes across the web then to leave it in for legacy's sake.
While Preran speaks for Adobe and gives the official answer, many within the community believe the reason why support was removed goes back to the reasoning of why Adobe bought Macromedia. Reason being that they cannot develop products around a proprietary technology, in this case Microsoft's, without their development lagging behind. And the other part of the reason was the numbers game. Based on 2 recent surveys ( http://news.netcraft.com/archives/category/web-server-survey/ , http://w3techs.com ) only 20% of servers run ASP/.NET.
Since that decision was made in 2008 to discontinue .NET support, I would typically recommend that someone invested in ASP technologies to use what was Frontpage, and then Expression Web and now Visual Studio Web Designer ( http://www.microsoft.com/visualstudio/eng/products/visual-studio-expre ss-products ). There's not really much else I can recommend that comes to mind.