Actually half of Catherine of Aragon's births were sons, and 2/3 of Anne's were sons. The problem wasn't that they couldn't produce sons, it was that the sons didn't survive.
Henry VIII had 11 children. 6 of them were (believed to be) sons, 5 were (believed to be) daughters. One of his daughters by Catherine was a miscarriage, the other stillborn, while one of his sons by Anne was a miscarriage. He also had one unnamed son by Catherine who died within days, and two sons - both named Henry - who died by 2 months. There was a son by Anne, also named Henry, who died soon after birth (if he wasn't stillborn).
This seems to indicate that in all actuality Henry and his brides had no problems conceiving sons, but at some point in fetal development or after birth the sons died. Not necessarily his fault.