The awarding of honorary degrees is a longstanding tradition at universities. In general, honorary degrees are designated in such a way as to make it clear that they are honorary, and not based on academic requirements. I served on a university senate for many years which approved such degrees as well as the criteria for granting them, and briefly on the specific committee (not my favourite committee work). At that university, all academic doctorates are PhDs, and all honorary degrees have other designations (most often LLD, honoris causa, which is what Virtue and Moir are getting from Western). While V&M don't have a particular connection with the university that I know of, they are locals who have had major national and international achievements, which are usually strong considerations in awarding honorary degrees.
(BTW, I do support the idea of honorary degrees in principle, and see nothing wrong with this case - but it does bother me that universities seem to be awarding a lot more of them these days. Possibly because there a lot more separate convocation ceremonies, and they seem to want to have at least one recipient per ceremony, but I think it devalues the honour somewhat)