A year or so ago before the launch of K2 we had the usual "Prediction of sales" thread.
Here, let me remind you all..
http://www.vgchartz.com/forum/thread.php?id=51641&page=5
At the time many would have taken anything around 2m has a great result.
They were many who thought it wouldn't get anywhere near 2m.
Ignoring the stupid sales estimtes from those who we now know to be anti-PS3 and were stealth trolling I would say many were spot on.
Don't forget, hindsight is always in 20:20 vision and it is easy to complain about sales now.
On a personal level I too wish it had sold more because I like it so much, but in reality that don't mean toilet.