We had the same exact stuff happen at the beginning of last generation. People constantly referred to Amazon, Bestbuy and Gamestop's top sellers. We had weekly annecdote threads. They were almost always wrong. I'm not saying that the Playstation 4 isn't going to outsell the XB1, but using these sources as a validation for that opinion is completely misguided.
You're being skeptical without being analytical.
It's correct that the current trends in pre-orders will not perfectly, or perhaps even strongly, predict sales at launch, but it's a rational basis on which to make a prediction. The alternative is to throw up your hands and say "there's just no way to know what people are thinking!" which obviously isn't true.
If you have real evidence that people were all wrong at the start of last generation, and the top-seller data was completely non-predictive, you should present it. There's a substantial difference between popularity on major retail sites and gamestop pre-order anecdotes. If your argument is that there were lots of gamestop anecdotes that amounted to nothing, you don't have to argue because I agree that's not very useful data.
A more general note of caution is warranted, though, in that GAF, in aggregate, is on a Sony train right now, and every little positive thing Sony does is likely to get spun as more positive than it really is, while every little bad thing MS does will be seen as even worse.