Actually, special units do have officers or sub-officers ranks. For instance, french fighter pilots are, at least lieutenants (if I remember well), as does naval frogmen. The reason is that those jobs are realy hard, dangerous and it's the only way for the administration to reward properly (financialy) the boyz.
Moreover, flight attendants got a rank too, because they (the women) need to have some authority over grunts during the flights.
Finaly, it's the same in several fictions. Every double-o agent, like Bond, is a Commander.
To my mind, it is logical that every membre of ou "dream team" might be well ranked, as they are part of an elite force of the Xenonauts project.