The game originally was going to allow you to pretty much recruit anyone at any time. However, the limitations of the 360 and the desire to avoid excessive disc swapping (as I recall) led to getting one set of recruits and then another.
Yeah, I guess. :D
Anyway, I did the Lair of The Shadow Broker mission which was pretty freakin good, everything with Liara is awesome, I think I'll romance her on my second playthrough.
Also, I wish you could recruit Legion earlier in the game, he's such an awesome character but there's not much him.
Legion / Tali = Best Squad.
This has been proven out by dialogue found from squadmates in missions where they couldn't possibly be part of in the released version of the game.