You're right it's not huge but (in hindsight) it's not negligible either. Because the vesting schedule is 4 years for each grant, the employees have no choice but to leave the shares in GOOG for 1-4 years.
That's not quite right in general. I had monthly vesting when I was there with a short cliff (I don't remember how short, but <<1yr). Shares appreciated according to the initial grant, regardless of cliffs. My previous comment glossed over the benefits/costs of borrowing against future earnings (note that typical RSU situations are effectively a 0% interest loan in a particular security), but that doesn't seem relevant to your rebuttal.
Each month of vesting you can absolutely move shares out of GOOG (minor restrictions on insider trading, but regardless of your level you can set up automated strategies), and most employees probably should given the correlated risk between Google taking a nosedive and employees losing their jobs.
The vesting is unrelated. With no promotions or raises the 4yr bump is uninteresting. With those, they match your TC, but they happen _during_ those interesting career events. They describe some subset of your compensation for the next 4yrs. You can still invest them however you choose. You can still leave at any time (unless you believe that in your personal case the promotion train is better than the job-hopping train). You could have just as easily job-hopped and invested the surplus in GOOG.
