There's not a lot of information so this might not be entirely accurate, but I thought this post from the HuniePop twitter account was interesting:
https://twitter.com/HuniePop/status/557692823450177536
If true, that basically opens Steam up to AO content, if that content is locked behind a "patch" like in HuniePop.
It has been popular lately.
I know Sunrider and Everlasting Summer do it too.