Not to that the outcome would have been any different, but Hughes had taken two or three solid dick kicks prior to the big head kick. Im willing to bet that if you kick someone in the junk enough, protecting there junk is going to become a primary concern and he might have been a little less wary of head kicks at that point.
Hughes took one kick to the groin that looked reasonably solid. Like another poster already pointed out, Hughes admitted after the fight he was bullshitting on the second one, his legs were hurt. You can also see that GSP knows this too, he looks at the ref and throws his hands up on the second 'groin kick'.
Hughes used this as an excuse when they did that big countdown of the 100 best fights, claimed getting hit by the groin kicks affected him, but that contradicts his own statements earlier.
Basically Hughes was just making excuses, thats how he is, he never admits he got beaten because the other fighter was better. GSP set him up with low kicks and caught him high later, I don't think the one groin kick that actually landed made any difference.