Of course the odds of having a gay son increase the more sons there are. One could also say that the odds of any one male in a random group of males being gay goes up the more men are in the group, too. The larger the (reasonably random) group, the more likely there will be at least one guy in a given sub-group, be it gay, or color blind, or left-handed, or...

Or, the analogy that the odds of rolling a one on a die (d6) are 1/6, but the odds of getting at least one "one" increases with the number of rolls. Roll enough dice, or gather enough random men into a group, and the odds of getting the event in question approach 1:1.