Two reasons I don't think is true:

First, how much harder is it to spoof actual devices, and take the time to spoof usage on these apps, vs. what it takes to spoof a single review?

Second, add to that the fact that spoofing 2000 app usages compared to the several thousand (or hundred thousand?) actual real users where real usage is being collected from. If you spoof 2000 reviews -- which are super easy to do, can be done in a matter of minutes with no long-term overhead -- you are aggregated with a much smaller number of real reviews actually being submitted.