Honest question - who cares? Someone actually used the built-in media player? Step 1 for me on any new desktop/workstation install (regardless of OS) is to install VLC.
I have to believe the number of people who actually use that can be counted in the tenths of a percent of their user base.
Among people I know, I can think of a few who rent DVDs from Redbox and watch them on their laptops (we're out in the country, so the internet isn't fast enough for streaming video). They're not technically adept enough to know that they would need something like VLC after this update.
I would care if tbe Xbox one, which will soon be on Windows 10, stopped playing DVDs. But I don't think this would be the case, there is probably a specific player for it.
I have to believe the number of people who actually use that can be counted in the tenths of a percent of their user base.