This is not true. Many of the apps are designed to be great on desktop PCs (as well as mobile ones). I use the Music and Videos apps all the time on my desktop at home (and Music pretty regularly at work). I also use Mail, my own Foursquare app, Messaging (mostly when people FB message me), Modern Reader, and that's not counting the ones I use mostly for the tiles (Weather, Calendar, etc)
The apps you list are some of the worst examples of Metro apps. If I want to play an MP3 the last thing I want is for the Music app to take over the entire screen for what is essentially a background process - I then either have to snap it to the side or task-switch out of it. It's the same when playing back videos - on the desktop I can choose whether VLC starts fullscreen or in a window according to preference; with Videos it runs fullscreen or can be switched to a useless side-snap mode. Mail wastes screen space to an absurd degree, especially when my desktop monitor is 2560x1600. Even Solitaire - which is a well designed app - is hugely constrained by the Metro design model, meaning you can't have it open alongside a file transfer or a browser window.
Microsoft should have allowed Metro apps to exist within the desktop environment - that is allow them to scale and feature the traditional window chrome. Then users would have had a choice at how they use apps. Instead Microsoft decided to dictate to users what they can and can't do and it's frankly insulting to anyone familiar with the Windows platform. Windows 8 is a great operating system on the desktop but the integration with Metro is shocking, without even going into the anti-competitive nature of preventing Metro apps from being distributed via other stores. I'm torn on the start screen, as it offers a lot of very worthwhile improvements (utilising the entire screen; easier arrangement of apps; greater visual customisation; live tiles) but still comes across as somewhat clunky when used with mouse and keyboard (I've been using it for over 6 months as my exclusive operating system).
Windows 8 might be great on tablets but Metro apps just don't work well with a desktop computer, especially not with high resolution displays. I wouldn't go as far as saying it's a tablet interface but I would say that it's a bad interface for keyboard and mouse. Oh, and the charm bar is terrible.