Playing against the AI on various difficulties is actually incomparable to playing against a human. The AI acts in an already programmed way, which makes it easy for the human to adapt. The only way you can get better is to play versus a human, and adapt to the different scenarios / builds on the Ladder.
Playing against the AI, is solely for you to slightly improve your own skills, and trying out a variety of builds.
The fact that you can beat the AI on the hardest setting, simply means you have a broader understanding of the game mechanics, as an AI on Very Hard is harder to beat, which makes you better than you where when you started out.
Any player who didn't start out by playing versus an AI will as a minimum get into Bronze league.
But a player who played versus the AI, is more likely to know more about game mechanics, which could place that player in a higher league - because that player, will beat the player with lesser understanding of the game mechanics.
My point is that its difficult to compare the AI to the Ladder.
You can have players who have never played StarCraft before, and get placed in Gold or Platinum. (I have a few friends who did this)
TIP: Play your 5 placement matches when you access HOTS, and then take some unranked matches for you to get used to your league.