I don't think anyone really expected the kind of performance the Wii U has had. Even people who were bearish about its chances generally expected far more than it actually sold. If anything, people who put thought into their predictions were probably less likely to get them correct. Prior to launch it would have been pretty difficult to argue that the Wii U would be doing worse than the Gamecube. Someone who just threw out a number would probably have a better shot at being accurate.
It is amazing how often people labelled as "haters" or "trolls" actually expected the Wii U to sell more than it has so far.
To put some numbers to this, there were 76 predictions for 2013 in this thread. The lowest Wii U prediction was more than 20% higher than the actual sales numbers. The average was about 188% higher.
http://gamrconnect.vgchartz.com/thread.php?id=152117