That would be about my best guess too. Don't confuse albums sold with records sold either. You will hear claims of the Beatles or Elvis selling 500 million records or something like that, but that is counting every single and album and everything... And since no one really buys singles anymore, we only really deal with album sales.
Well MTV Europe had a U2 weekend when POP came out and they said "over 75 million", when ATYCLB came out they said "over 80 million". U2's Story in music - included ATYCLB - said over 100 million.