Thats a basic pay chart - does that include X-Factor?
Also bear in mind that when on deployments a lot of allowances kick in, boosting pay, as does trade pay or specialist pay. I know of very few guys in the forces who only get the basic pay band. Add in fun things like boarding school allowances, missed meal allowances, free travel in London, subsidised accommodation, an excellent pension/gratuity etc and the packages value adds up considerably.
CS do not recieve X factor, are only paid for days worked and as such need a salary boost when deployed to compensate for the change in working conditions. Seems fair to me - I can imagine the screams of protest were the MOD to do away with X Factor for personnel who deploy.