the 48 month vesting schedule described above (resulting in approx 12% figure) is a very typical vesting schedule. Industry standard might not be exactly the right term, but it's probably the most common default/boilerplate plan.

edit: from the parent:

A typical vesting agreement would have vested your stock over a 48-month period, so after 18 months you would have vested 33% x 18/48 = 12.375%