I agree that the rank of Shodan is often earned earlier in Japanese Dojo than in dojo located in the United States or Europe. I also agree that in the United States and Europe, the rank of Shodan is often looked upon as rank that denotes expertise or "mastery" in an art. All one must do to understand this is to strike up a conversation with someone (outside the realm of martial arts) and talk about your art and tell them that you are a black belt. I'll bet that the person with whom you are conversing will assume that you are some great martial arts master because you are a black belt. I believe a lot of this thinking has to do with the media / movie interpretations of martial arts and those who study them.
It has been said by someone on this forum before that if you compare a newly ranked Shodan from Japan (an individual who has earned their Shodan in say, about a year) with someone from the United States or Europe (an individual who has earned their Shodan in say, about 5 years); the newly ranked Shodan from the United States or Europe will most likely have better form and function of technique. I have no doubt to this having some validity. I've had the opportunity to train with both types of individuals and my claim (and the same claim by others) has held true.
At the same time though, it has been said that at the higher Dan levels, the Japanese students seem to have better form and function of technique than those students in the United States and Europe. The reason for this is probably a stronger dedication to the art by the Japanese students. It seems that since many people in the United States and Europe equate a Shodan or first degree black belt with expertise or mastery, they feel as though there is not as much to learn after that rank is achieved and hence, do not continue on the path to greater technique and wisdom.
Of course, this is all my own opinion and the forum readers must take it for what it's worth. Let me know what you think about what I've written. Have a good Day!