Usually when numbers are presented that way it's because there are many studies they looked at. So I presume there was one study showing a rate of 40%, another showing 70% and the rest of the studies fell somewhere in between those two extremes, with differences likely due to types of games, types of systems, and any number of other factors, including chance. They could have just averaged all the studies and quoted a number like 55% for example, but I think the other way actually paints a better picture of the data. It's still possible they're full of shit, but just presenting the numbers like that doesn't mean they're pulling it out of their ass.