Genuinely wondering what commitment you're speaking of. I've worked for some big names, in several states, but my employment has never had any commitment attached to it by the Employer.
If a company extended you a full-time job offer knowing that they were only going to use you for 2 months and then get rid of you, you'd be pissed, and so would HN when you told them about it. People would be disinclined to accept job offers from that company, once they found out what happened.
Legal commitment isn't the only kind of commitment.
Understandable, but I've seen several people let go because they didn't mesh with a company culture, within a probational period, and I think if it were me I wouldn't hold any hard feelings if such a thing were to happen.
In a situation where everyone is negotiating in good faith, when a company offers you full time salaried employment they're expecting you to stick around for awhile. Depending on the company, this could be a year, two years, ten years. They don't expect to terminate your employment themselves. That's the commitment tptacek is speaking of. They're committing to buying all of your available work hours for an semi-defined period of time in exchange for a regular paycheck. Their legal commitment to you is generally extremely limited, but also not relevant to this discussion.
In consulting/contracting/freelancing terms, if a client accepts a multi-year retainer with a large number of hours, you'll likely give them a bit of a discount relative to your normal everyday rate. They're committing to continuing your business relationship for the duration of the contract, even though the contract will almost always state that either side can end it at any time with a certain amount of notice (just like full time salaried employment).
