I believe that the written offer letter helps you seek damages related to relocation, losing health coverage, etc., due to the expectation of starting a new job. At-will employment lets you fire people without consideration, but it doesn't let you scam them into investing their time and money into the business relationship.
This is true, but I think everyone would be aware that fighting a court case as a recent grad will be far too expensive, and doing that from outside the country adds even more on top.
