There was a thread on hackernews a few days ago (maybe even yesterday, time is a construct) where someone shared a screenshot of a pop up ad served to them by the OS itself.
Seeing a very popular and powerful $5 OS next to $100 Windows cards at the store would be pretty compelling. I guess their advantage would still be that all you need is a code to install Windows on many machines while you need to boot into an external drive to install Ubuntu (and any other OS).