I think in IT you are creative person and you can't create more than you want to. You can be extremely productive but there is upper limit. If you get 10 days and don't get 28 days like European you get that 18 days in some other way.
There are about 15 national holidays in Japan. Also, if you stay at the same company (which most people tend to do if they can) you're entitled to an additional vacation day every year up to 20 days. So a person with a 5-year tenure will have 15 + 15 = 30 days a year.
