Some guys don't care about stuff like that, especially if your not looking into having a serious relationship. It's a different mindset and kind of hard to explain. Obviously if your serious about someone, you take their past history (including sexual) into account but if not, that's what condoms are for.
A friend of mind was like that (slept with a lot of women) and I asked him one time if he ever thought of settling down and his answer was, I'd like too, but then I see a hot girl walking by and I just got to have that.
I know the women on this forum will find that gross but some guys think like that. Case in point, I saw a guy name his fantasy football team the 'Casey Anthony MILF All Stars'. True story.