yeah, I am also sure it's not unlimited time for the offer, so I am pretty sure it's only for a fixed amount of time, say 12 or 24 months.... notice even the child support/subsidy and the children medical fees are until 12 years old only.
Additionally, it will be kindda of loss of face if your friends neighbours knew that you were on the "free handouts" from the govt.... right?
At least the Japan govt is willing to help its citizens, that's quite unheard of in today's capitalistic world.
In any case, I heard it is extremely hard to qualify for Japanese citizenship. So that automatically rules out a lot of new immigrant's dream of leeching of the Japanese govt's kind gesture.