I think you are right--that an actor is smart to never turn up their nose at auditioning. Some actors are smart enough to want to make sure they are right for the part. But most of what an audition is, is the chance to get to know someone: their talent and their persona (are they great to work with?). "Stars" have that covered. If you know that Nathan Lane will be perfect for a role--you don't need to audition him. If it is a stretch for a performer--then maybe. But, you don't have to audition these people when you KNOW they would be great for the part--or interesting in the part. And if a star wants to play a role, and has the money/clout to put that show together--than good for them. They may have to deal with bad reviews and a flop, but I don't blame them for wanting to make parts happen.
The same is very true for film.
And, no, auditioning ISN'T always fair. #1 rule of being an actor should be getting over the auditioning madness. People get cast because they are a star, a friend of someone, a lover of someone--whatever--quite often. Sometimes it produces crap and often, things are prob fine. But a good chunk of casting is connections.
:)