An explanation that says all observations are equally likely is hard to disprove and hence hard to gather evidence for by conversation of evidence, but that doesn't mean we should give it an extra penalty.

You shouldn't give it an extra penalty. He's just using an unusual method for explaining the first penalty. The penalty due to the fact that the friend who has all colors of marbles is less likely to drop a black one is equivalently stated as a penalty due to the fact that he has more possible colors he can drop.