I have had spam the last two weeks, as have my ice and daughters on their iPhones. I think I've gotten three messages, and they have gotten about the same. One of my daughters was with her softball team when they got an ad and everyone else (I think it was actually iMessage and Android devices which got this) got similar ads within ten seconds.
The thing is, you get a spam message, and you just delete it. It is annoying if you are on a limited-SMS plan and have iMessage turned to SMS-only, but the volume is too low to worry about at this point.
How is the BBM paradigm of you get a "Let me send you a message" request and accept it (because you don't know if the person on the other end is someone you legitimately want a message from or not since there are no message contents in this initial inquiry) followed by the same spam message any better? Seems measurably worse, IMHO. At best, it is "different" but definitely not any better.
Looking at the study, 30% of spam on iMessage seems lower than the percentage of iPhone users, at least in the US. I'm not sure why this is surprising. As I said above, spam messages are hitting all messaging providers, and BBM's technically-not-spam approach provides no protection at all.