I would never claim that, for the simple reason that there is ad spam on JP servers. Just less of it and all in the English-like language that the spammers use to bypass text filters. There was a thread here last week complaining about it.
To answer the spirit of your question though, no. I'm not saying that they aren't enforcing them. That would be a frankly libelous thing to say, they are trying to enforce them and failing miserably. I do believe that they are more diligent about enforcement on the JP servers. I stand by that statement.
The anti-RMT efforts are better implemented on JP servers than they are on NA servers. The biggest being the text filter. The reason the messages come through looking like gibberish here is that they are written that way to bypass text filters on /tell /shout, etc. SE so far has been throwing that and reporting as the solution to the problems on the NA and EU servers and it's crap and they know it is. The English/French/German filters are too easy to get around.
To turn your question around on you, are you claiming that there is something inherent about being a Japanese player that makes them less willing to look for a shortcut?