This seems ludicrous. First point is that I'd say it doesn't really impact on jobs. A politics graduate can go on to do most high paying jobs potentially - banking, finance, law, consultancy.
I think people wrongly assume that people HAVE to have a job related to their degree, which is of course very naive and, basically, wrong. Perhaps people doing science/engineering do not like the thought of someone doing better than them in the employment world without having to have studied something that didn't bore them to death. (Now, this won't be the case for all science students of course, but many simply to engineering, for example, because they think it will lead to a high paying job, when in fact there are far more that are more lucrative if that is what you're after.)
And to the person to wrote about Chinese and Indian students not coming over to do Politics - that is a complete misunderstanding of culture. With my other-half being Chinese x Indian and my friendship group being mostly Asian, I can tell you that the reason they don't often come over to study Arts subjects is that it's simply not in the culture. There's a greater emphasis on taking an education that DIRECTLY leads to a job BEFORE you even start university. Some areas in their respective countries are still developing, so the emphasis is on doing something where they can SEE immediately where they will end up, and thus have job security and in turn financial security. Even in the cities where these countries are very developed, the culture persists simply because culture doesn't die quickly.
People need to broaden their mind and stop thinking they have to make career choices are A Level.