Why no Surface RT sales numbers?

Does it bother anybody that Microsoft has commented on it's Surface RT reviews or why they haven't released figures of their flagship tablet?

They didn't get the best reviews but reviewers highlighted a lot of great things to be mentioned about the Surface. Capture_png_medium

via lh6.googleusercontent.com

My personal guess is that they sold 600k units which is enough for them to call the launch a success but not enough for them to compare to iPad or Android numbers.