Two entirely separate and unrelated points.
An RAF College degree would be relevant, and would have lot's of other advantages, but you'd end up with guys who had seen nothing of 'life outside' between school (perhaps a fairly monastic/sheltered/institutional boarding school) and the RAF. Surely the benefeit of having graduates from a variety of Unis and Polys is that you get people who've had excellent (often irrelevant but academically and intellectually stimulating) training in their chosen subjects, who have seen a bit of 'life' and who have had to relate to and live alongside people from very different backgrounds with very different values and aspirations. They are, I believe, more likely to be 'rounded personalities' and as such may give the RAF as an organisation an essential understanding and linkage with life outside, where, of course we all sit down throught the national anthem, don't drink, smoke prodigious quantities of weed and vote loony left. I wouldn't want evry young aircrew trainee to have come from a asket weaving degree at Hull Uni, of course, but a handful are useful.
Secondly, UASs are the single best way of winning friends in the Uni-educated world - Many Drs, Lawyers, Teachers and filthy scum journos look back on UAS days as 'the best in their lives' and are left with an abiding affection for the RAF, a vague understanding of how it works and what makes it work, and an enormous respect for it and its members, and all for the cost of between one hundred and fifty and two hundred hours on the Bulldog and/or Chipmunk. (Oops! Am I showing my age and hours-hog tendencies?)