It may be common knowledge inside the beltway, and believe me, I have plenty of gay friends and family, however I was struck how he used it as a wedge between the administration's position on gay marriage and Cheney's personal relationship with his daughter. I thought it was a cheap shot in the worst way.
Cheney should have remarked regarding healthcare that even though you love your wife, she is unhealthily too heavy and we shouldn't have to pay for her healthcare, but it's nice that you love her anyway.
It was all over the lamestream media earlier this year when the gay marraige issue was hot. Cheney made comments in the press at that time regarding his feelings on the matter. It was also brought up several times in 2000.