Actually, Japan's immigration rules are extremely relaxed. For "engineers" (programmers qualify), if you have a degree and a job offer, you're good to go. The new rules even allow a 5 year visa which doesn't necessarily terminate if your job does. If you are a native English speaker (you have to have 12 years of education in the English Language), have a university degree and a job offer, you can teach English. Other categories exist for business owners, etc.
I haven't looked at every country, but I think Japan is probably the easiest country to come and work in the G8. Why are there so few foreigners? Culturally it's hard if you are inflexible and you don't speak Japanese. Even though there are actually quite a few jobs available for English only speakers, Japanese culture is really linked to the language. I don't know how to explain it properly except that there is "inside" and there is "outside". If you only speak English (or Japanese poorly), you will always be "outside". Outside is sometimes kind of nice because nobody has any expectations of you. But similarly, you get few benefits. You're always the hanger on, never part of the in group.
Even without language issues, many people have difficulty because Japan is an intensely moral culture. There are things that are absolutely morally right and absolutely morally wrong. The problem is that these things are often quite different than what is morally right and wrong in the west (especially the US, which is also a very moral culture). People from some certain cultures seem to have a great deal of difficulty dealing with Japanese ways of doing things. Not necessarily a bad thing, but not great if you want to live in Japan :-)
Anyway, if you want to work in Japan, and have a university degree, you can do it. One last issue... The Japanese work system is really different. You get hired after university and you stay at your job forever. It's really hard to get a regular job if you aren't coming right out of school. It's nothing to do with immigration policies -- workers whose companies fold on them suffer too. This is why you get stuck in a "temp" job. It used to be that "temp" workers often got stuck with 1 year visas, which were renewed every march. If a company wanted to get rid of foreign workers, all they had to do was make it known that they didn't want to have the visas renewed and problem solved. But with the new system (starting next week, I think), they can no longer do that. Visas are 5 years and usually extend past the end of the job.
The major downside for having a "temp" job is that usually you don't get paid a quarterly bonus or certain benefits. If you are a programmer, you can often negotiate these details. If you are a teacher, you can't and you will end up getting paid about half of what regular teachers get paid. However, the responsibilities are *much* less, so personally, I can't complain about it.
Anyway, I live in Japan. I'm actually off abroad for a couple of years so that my wife can learn to speak English, but apart from that I'm here permanently. It's my home now. People here are friendly and welcoming of foreigners if you try hard to fit in.