My personal opinion is that babies and toddlers are supposed to be obsessed with them...not grown men. LOL! I always remember that anecdote from the anthropolgist talking to a group of mothers in a tribal village (Africa or South Pacific? Can't remember!) who mentioned to them that if women in her culture (Western) walked around with no top on the men would get all excited. Apparently they all rolled around laughing, saying in disbelief 'What grown men act like little children about boobs??'
I think your DS is just showing his appreciation for them and the time he had with them. Completely normal in my eyes. Although I completely understand your getting tired of it. It can be tiring having little hands reaching for them all the time!