Seems to be this is more related with the gender distribution in each major more than anything else.
Engineering and sciences have a high percentage of males vs females. Therefore is logical to think that any woman in that field has a lot of possible partners to choose from.
That's probably part of it. But I also think it probably has to do with "ways of thinking." A person who chooses engineering as a major often tends to "think a little differently" from one who chooses math and physics, for example -- some people are more oriented toward "practical" solutions, while others are more interested in abstractions and "theory." (Obviously these are broad stereotypes, but they do have some basis as generalizations for many people.)
Even more extreme divides in "ways of thinking" come about when you start comparing things like religious studies to engineering or whatever. The people who are attracted to these majors have very different outlooks on the world. It's NOT surprising at all that they'd look for a spouse with a similar worldview.
Relationships are also about communication. We often hear jokes on Slashdot about the problems "nerds" have communicating with others, so again it's unsurprising that people who "talk the same language" will be attracted to each other.
So, I really take issue with the conclusion here, as TFS says:
The blog concludes that your choice of major may unwittingly decide your choice of spouse, and depending on how well that field is paid, your economic future.
No, no, NO. Your choice of major won't "unwittingly" decide your spouse -- your choice of major is partly determined by who you are, how you think, how you communicate, and what your interests are. People who have very particular ways of thinking (particularly ones that lead them to cross stereotypical gender boundaries, like female engineers or male nurses) will probably find it harder to find compatible spouses among the more "generic" general population.
Or, to put it another way, if you're already predisposed toward majoring in something like religious studies, simply choosing to be an engineering major isn't going to stop you from thinking deeply about religious issues. And you'll probably continue to want a spouse who is at least somewhat interested in thinking about those issues too (engineer or not). The causality here isn't only the major -- it's the reason why people choose their majors in the first place.