Ignore the "cool wives" Op and the "they're just breasts" comments. We ALL know that there's a huge difference between men and women going topless. Women's breasts are sexualised, this is why women don't wander down the road topless, or do their weekly Aldi shop with their tits out. I mean, where do you draw the line? What if the colleague comes round for a BBQ and goes topless in the garden? Is that ok? If not, why not, they're "just breasts" after all.
I think that some women forget or choose to pretend that men and women generally view breasts differently.
Anyone who has spent any time with men will know exactly what men's reactions to breasts are - underboob, side boob, full boob, cleavage, "haven't seen the tit until you've seen the nipple." And its not something they get less interested in as they get older either. The sheer amount of female nudity films/on TV, porn, strip clubs, OF shows that.
Even men who wouldn't seek it out are just as happy when they see them.
And you'd be a fool to think otherwise.
So, yeah, be happy with it if you like but don't kid yourself that he's not paying attention, committing the image to memory or concealing a semi. Because he is.