I wonder if the reward mechanisms factor in denying resources from the enemy team. A lot of the time it makes sense to take Roshan just so the enemy doesn't get the opportunity to.
I think that'd be an even harder behavior for the ai to come to though, since they'd have to recognize those benefits for the other team and their origin, and then finding that taking Roshan prevents those benefits. I think that's a next step after discovering the benefit of taking Roshan.
Same argument applies to pushing and defending towers, getting rax etc. Assuming that the devs did not hardcode rewards for those objectives, then the AI surely already has to 'understand' events that impact the game in long term.
I think you're right about it being more about denying the enemy team. IIRC, in the last update they said that the bots tend to prioritize denying creeps and taking objectives over getting perfect last hits in lane.
