The primary benefits of the Windows certification program, like the one for Windows 8 and Windows 8.1 before it, are inclusion in Microsoft marketing materials and the ability to submit your application to the Microsoft Store (which JRiver is unlikely to do for other reasons).
Going through this certification process involves, primarily a ton of paperwork, and a non-trivial amount of cost (because time is money).
Alex, the information you're linking to is primarily the process and requirements for certification, not the benefits to the developers, which Microsoft loosely enumerates here (though it seems they haven't bothered to make a new page for the Windows 10 certification process yet):
https://msdn.microsoft.com/en-us/windows/desktop/hh968450.aspxAs I said before, it is primarily a marketing scheme. In some cases, it might be worthwhile for applications to go through the process, especially if they intend to target new functionality primarily targeted at Windows 10 (such as making a Universal application). Or, perhaps, if they have enterprise customers that require it. This doesn't really apply to Media Center (which is cross-platform focused), and also doesn't apply very much to an application that has existed on the platform for two decades.
In any case, you asked the question, and got an answer from one of the lead developers (Hendrik). JRiver does not believe that certification through Microsoft provides substantial developer-facing benefits to outweigh the substantial resource commitment that it would require. Thanks for your thoughts, but I'm going to lock this now.