In a smaller country like Denmark, it seems that gay people in the rural areas might just move to the city where attitudes are more accepting.

This is also fact in big countries like USA. Here a survivey whith praevalence and factor residence place: Stuart Michaels 1996 Table “Wohnort” = “place of residence”, “Vorort” = “suburb”, CC = Central Cities, biggest metropolitan areas, “Nächste 88 CC” = “next 88 CC”
There is also a little study from a country youth organisation around Berlin. And a residence study in Vienna (wich place in the city, gay neighborhood) where overproportional people are born in rural areas.
The Causes are different. Some move to a big city before coming out, because they feeling not right in the social tightness of a small town. But it is only one factor to move. It makes it more likely to move. The primary causes are mostly better worklplace, etc.
And same sex partnership is not prevalence of homosexuality. I think you will find also more homosexuals in traditional marriages in urban areas.
For Trayce Hansen from NARTH this study is an evidence that Legalizing Same-Sex Marriage Will Increase Prevalence of Homosexuality.

There is a slight increase in odds of homosexual marriage for men if one’s mother was over 35 at birth.

I bet if I googled for even 5 minutes I’d find that 100 different health problems go up for children of older moms.
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One of the first developmental markers scientists check for is handedness. Do older moms have more left handed children?
Lefties more likely from older moms, study says
Check! For those who don’t know an increase in left handedness is a sign of misdevelopment. For example half of all premature babies are lefties.

I find myself in the unusual position of qualifying Morten’s conclusions. I think there is a need to qualify the factors by the non-significant results found. For instance, Morten lists father absence as a factor related to gay marriage. However, I would note that paternal absence via death was unrelated to outcome as was lack of knowledge of father’s identity.

When the father relationship plays into the picture, I don’t think it’s absence as in death, divorce, military service, etc. I think it’s more of a message that a child perceives from a father who is present.