This has been addressed by the dev team here.
TL;DR: there’s a bunch of minute differences, none of which should affect sound quality. The only significant difference I can think of is home automation integration, but that’s something for which I find the upcharge not only completely fair, but also rather sane.
If anything, that Roon offers a downloadable image that allows you to DIY a device some of us think is way too expensive, alongside with support for said image, speaks highly of them, their confidence in their product and in the value of the service provided with it by their retail network. And to go back to the Apple analogy, I don’t exactly see Tim Cook ordering his teams to make life easier for the Hackintosh crowd.