That's not really relevant to the question asked there: You don't need to own an Apple product to buy music trough iTunes.

If you wanted just that one song then iTunes was very much the most affordable, and accessible, way to legally buy digital music back then because it only charged you $1 for a song.

The only other alternatives where, often legally rather obscure, flatrate subscription models or buying the physical full album, which would usually have cost you at least $20+

Valve did something very similar with Steam: Very easy to use and it actually passed on the savings from digital distribution to the consumers by heavily discounting the prices of games.