Well, the bikes you're thinking of are what they call Supersport class. While they are basically stock bikes just like the ones you can buy, they have numerous modifications done to them.
All of these mods are simple things that you, as a regular street rider, could easily do to your bike, with enough money, and a good tuner.
The reason they do such effortless wheelies (in addition to skilled riders, who pretty much make everything they do look "easy"), are things like exhausts, jetting, valve jobs, different gearing from what the street bikes come with, bigger radiators (in World Supersport) for better cooling, and lots of dyno tuning for optimal performance.
Furthermore, in race trim, the bikes weigh a good 30 lbs. less than the street versions, due to removal of all unnecessary lights, brackets, accessories, etc., as well as bodywork that weighs much less than stock.
Add all this up, and you have some pretty wheelie-prone motorcycles!
I'm not joking. And don't call me Shirley.