Monsoon did it for years (hence the name "Gorilla position"). Vince has done it ever since he left commentary. For the most part, the commentators are left to raise their own points and push the ideas they are scripted to push. But, when there's a major story point to be made, they are fed lines or ideas that they will craft into lines.
The funny part is that Lawler now gets next to no feed (which is why he's quiet so much during Raw matches), Cole gets most of the face comments now (funny considering how much heat he got during his heel commentator run) and JBL gets much of the "company line" comments. It doesn't surprise me at all that JBL would be "the voice of Vince". He's generally a "company guy" and his actual personality is very close (but much more low-key) than his JBL persona today, and that personality is, in many ways, very similar to the real-life personality of Vince McMahon (right down to their political and business philosophies).
wk