I don't see that as a compelling argument, since generally these secondary characters aren't role played at all. Or if so, just in a minor aside which doesn't detract from the game at all.
GM: You come to a fork in the road. Do you go left or right?
Cleric: My faith gives me a feeling that left is the way.
Fighter: Arrr! My dwarven bones tell me treasure is towards the right...in the mountains!
Rogue: Let's flip a coin! Left it is!
Wizard: Um, hey, Binky, which way looks better to your feline eyes? *meow meow meow* Left, you say? OK, I say left!
I doubt the other players feel that they are being cheated out of any role playing. Of course, not that the familiar doesn't really have a say in what happens, it's just an extension of the wizard.