Difference is SimCity was supposed to be playable by everyone who paid for it upon launch, Dota 2 wasn't. The game has been easy to access for over a year now and you could have tried starting to get access when
this post was published and gotten 15 keys by now.
Valve never planned on letting everyone play right away, they told everyone that weeks in advance, there's no reason to complain about it. You could even have asked here any time for a key, I had a good 50+ keys spread across all my accounts. I'm sure anyone who waited for 2 years can wait a bit longer and anyone playing the game is happy enough about Valve making sure that servers won't fail us old players upon launch.