Yes, there is a reason for this. For example, consider pitch of an airplane. If the plane pitches up 20 degrees, then the angle at the center of the plane is 20 degrees. If the gyro is mounted in the nose...still 20 degrees. The entire plane is pitched up 20 degrees, so it doesn't matter where you measure this. So this leads many people to assert that the mounting point doesn't matter.
HOWEVER, notice that when the gyro is in the center, it is experiencing 1g all the time, independent of the pitch-up. If the gyro is in the nose, it will experience positive g force while pitching up, and negative g force when the plane is pitching down. Typically gyros will have some sensitivity to both g force and vibration, due to minor asymmetries.
Consider for example this application note from Analog Devices:
According to this, the g-sensitivity for cheap gyro (and anything in a model airplane will be "cheap"), can be about 0.3degrees/sec/G. Well, that is not a lot. If your plane nose experiences 3g during a 20-degree up-pitch in 0.5sec (that seems like a rather violent bump), then the rotation is 40deg/sec, and the error term due to g sensitivity would be 3g * 0.3 or about 1 deg/sec. That is only 2.5% error. Well, that is not a lot, but not insignificant either. And as you can see from the application note, other components have less G sensitivity.
So the bottom line is - yes there is some theory behind it. If you want to be conservative, mount it in the center. But I doubt you would notice the difference in typical practice. Also, different MEMS components are different, and it would take some research and calculation to figure out the precise significance in your application.