I bought music from Google once. They required that I use their app to play it online. I could download it in MP3 format, but I was only allowed to do so a certain number of times. (Four, IIRC.) Contrast this with Amazon which will sell me the digital music, let me play it online or download it as many times as I like in non-DRMed MP3 format. That's why all of my music purchases (except that one described above) are from Amazon and not Google.