I agree that the connotations are different, but the way the vesting is written into these contracts, it is essentially a periodic stock grant, which ends as soon as employment does, and with no guarantee that it will continue. In that way it's very much like a salary, despite how it's typically viewed. Perhaps the expectation part of things is strong enough that this could be considered bad faith, but my understanding has always been that if someone doesn't work out as an employee for any reason, they have no claim to the unvested stock.
Options are used as an incentive for employees to stick around with the company and to work harder in the hopes that their hard work will result in 2-4 years in a higher stock price (or high IPO), which benefits both the employee and the company.
Attempting to take back options which were promised in the past because the company currently thinks the employee doesn't deserve them is aptly named "claw back", because that's exactly what it is.
Imagine a company asking someone in 2011 to give back a part of their 2009 salary, or be fired.