Absolutely -- yes Windows came with your PC, but you'd buy the new version as a (cheaper) upgrade if you didn't want to wait until the next PC you bought.

Today new OS versions aren't such a big deal, but when Windows 95 came out, and then XP, they were huge, with total interface redesigns.

On the other hand, I don't think people went out of their way as much to buy smaller upgrades like Windows 98.