I am fairly certain you can't compare VGC to NPD because they group sales differently. You are probably looking at WW sales or Americas sales on VGC and comparing it to the NPD, which is not the same, and then trying to draw some conclusion.
Either way you are completely wrong about Sim racers. They are probably more popular, in terms of sales, now days then they were before. no racer touches GT and that game has yet to come out. When it does it will be huge. Other than that the Need for speed series has gotten a nice little ressurection lately, the burnout series has sold nicely, Forza sales pretty well also. I'm sure there are a few other sims out there that sell relatively well for not being a genre leader.
I don't recall any other period in time where racing sims just flew off the shelves besides the aforementioned Gran Turismo and maybe a time where need for speed sold remotely better than it does now.







