Hi aeric,
The main reason (at least for me) is that it simplifies "a lot" when you're build an app for a "non-internet" scenario and you need to have multiple devices reading data from a server.
Usually when we speak about http server on an android device, people think about "hosting a server" to serve websites or something... for me, that's not the case. It's just about having a simple API on the server that the clients use.
If we've powerfull and cheap android machines nowadays, why complication the instalation with an extra raspberry box? I totally understand ilan. I'm using it on Android (since my project is android based).
Cheers.