Not quite true: The other huge group of customers is simply gamers.
[1] http://www.literaturepage.com/read/thusspakezarathustra-107....
Now, we can't say for sure how many of these users primarily use their PC for gaming. But it's probably a lot of them. PC gaming is huge, and it's one of the few areas where a general consumer actually needs a PC, and can't use a phone or tablet.
[1]: https://store.steampowered.com/charts/
[2]: https://store.steampowered.com/hwsurvey/Steam-Hardware-Softw...