You have effectively answered your own questions. Cadets will be on reduced salary so in reality paying for their own training. VA gets to write off vat and tax of training costs upfront. Net result is they get 50 cadets that sing from the Virgin hymn sheet from day 1.
Every airline thinks that their sops and standards are the best. It's the nature of the industry. Moulding young impressionable wannabes from day 1 will endear them to stay. They won't be able to afford to jump ship to nasty big cousin BA as they are entrapped in a huge bond - we'll not unless VA goes under....
Top of scale salaries are for another day. Airline accountants don't think more than a few years ahead. The reality is that in 9 years time when they are off bond VA just like my own airline will no doubt have a different salary scale.