I dislike the wording. Clearly it's not 'unlimited', if you stay away for a year or four, they'll kick you out. It's 'unlimited' in the way that some 'flat rates' come with strings attached that make them very much not a flat rate because they'll just cut of the service if you cross some threshold.
Since Microsoft is a commercial entity, my assumption is that they've studied the policy's effects and found that many people will take fewer than 4 weeks if you ask them to "take whatever you need and what you feel is fair", so employees will feel that they've gotten a generous gift while Microsoft will make more profits.
Since Microsoft is a commercial entity, my assumption is that they've studied the policy's effects and found that many people will take fewer than 4 weeks if you ask them to "take whatever you need and what you feel is fair", so employees will feel that they've gotten a generous gift while Microsoft will make more profits.