This degree debate is a bit off thread but for my part I've always considered that the requirement to have a degree is simply a way for the US majors to filter applicants. In the US the degree needn't have any relevance whatever to aviation but does indicate that the applicant has demonstrated a certain level of intellect and is therefore less likely to fail academically.
The UK airlines adopt a less stringent approach knowing that the UK CAA implements a very much tougher ground exam regime for the ATPL than the FAA.