Windows Media Player vs. iTunes
In a nutshell...
The Windows Media Player prior to Windows 7 will play most audio files with the exception of the Apple iTunes format: M4a, m4p & acc. These file types are ignored by Windows Media Player. However, the WMP will launch a m3u playlist without complaints. Windows 7 and later will play iTunes files.
iTunes will play practically any popular audio file type. However, at this writing at least, it will not correctly launch a m3u playlist. It will play the first song and then stop. The work-around is to import the m3u playlist by selecting: File --> Library --> Import playlist in iTunes and browsing to the m3u file. The playlist file will be converted into the iTunes format where it can be launched in the typical iTunes fashion.