I think it's justified. People have better things to do than to investigate people fully (opportunity cost of time). I mean, if it's clear that the person is a bullshit artist, and the VU guy has more potential, and hence the employer favours the VU applicant, then that's also alright. Interviews are mainly an intuitive judgement process, and are just as judgemental as generalising based on the prestige of a university sometimes.
If these judgements are not effective ones, then that firm will simply fail to thrive and survive in the competitive marketplace, as they will be paying for duds, while the other firms are paying the same for better quality, due to a better judgement process, but it is unlikely that firms will jump to full investigations about their employees. They will resort to quicksnap intuitive judgements because of the lack of information available to them and the costs associated with obtaining the information.
It can be non-ideal, but I think generalisations are fine.