Perhaps you understood me wrong now.
The marriage laws have changed quite a lot. Today anybody can marry anyone regardless of gender etc. Therefore, also in many countries the immigration laws have changed, and marriage does not play a big role in the actual right to obtain a temporary / permanent residence. If you read the regulations (the current ones), they are very clear not to even mention marriage. I do not know why. The only regulation is that one can prove by fact that the parties actually are a couple, and that the couple have the financial capacity to maintain it (education, work and somewhere to live). Marriage it self does not prove that the persons actually are a couple (this is for reason you probably know). Also, with the divorce rates today, it is kind of irresponsible not to protect one self. However, as I said very few think about these things when they are in the state of mind of getting married (and the brain in in the pants). I hope that I am not cynical, but factual.