I'm not sure I follow that. If you're getting those shares instead of a higher salary, there's no effective difference between that and a cost you paid out of pocket (except for certain tax implications).
That said, legally, even in the specific case of the Shopify plan, you aren't taking cash and spending it on Shopify stock. If you were, your tax situation would be more complicated.
You do, it just isn't spelled out. If you're getting comp in one way (RSUs), then you're not getting it in other ways (salary). The same is true of other benefits, like free food, 401k contributions, etc. It generally isn't a 1-to-1 thing, but it _is_ a tradeoff.
I guess that's the monkey-paw side of "incentivizing the employees to make the company perform by giving them a stake in the upside"...