It's source engine, albeit with the updates source has received over the years.
I've gotten burnt out on being the only (decent) hard/semi support player in the last 30 or so games I've played. You can only buy every set of wards, set up 80% of the kills, and buy every support item for your team before you just get tired of getting let down by players with no situational awareness or game sense.
I do hard-lane solo a bit too, and it's extremely frustrating when their team sends 4 people at you and your team continues to afk farm jungle and safe lane.
RAGE DUMP
I do more than my share of playing hard support in pubs. Generally I wait and see what my teammates pick, so I get stuck with the role more often than I'd like. Last night I had a guy voluntarily pick Crystal Maiden as the second to last picker on our team, leaving me in a state of shock and with the option to choose any number of carries or semi-carries to lane with him. Went with Dragon Knight, we raped our lane, and cruised to an easy win.
After the game I checked to see if he was one of those dudes who always plays support, and he totally wasn't, so it refreshed my batteries as far as being willing to take one for the team and roll support more often than the 20% of the time that would be equitable if every Dota 2 player were as reasonable as you, me, and the random CM I owned with yesterday.
I'm also thinking of queue'ing for Random Draft only, as I tend to get better team comps and more people willing to play support when I play that.