Even the smallest company I worked for (about 100 employees) had immediate 100% vesting, but other places have all been significantly larger. The big boys, Lockheed, Raytheon, Boeing, Northrop, all have immediate vesting. And the mid-size companies I am familiar with do as well.
My guess would be that the intense competition among the companies for qualified engineers and scientists is what leads them to offer 100% immediate vesting. It’s quite common to jump ship, although the current economy has slowed that down a bit. Benefits are certainly a consideration of employees shopping for a new company.
I can’t remember what the government labs offer, maybe its the competition with them that leads to the immediate vesting plans.
Yarster, companies or divisions that have poor management quickly lose their competent employees. As an example, I know one company that started treating its employees poorly. They lost basically all their engineers and got their government contract cancelled for failure to perform. I don’t know the fate of those managers, but debooking a multi-million-dollar sale cannot look good at a performance review. As a rule, managers are competent in this industry.