I can't say I'm an expert, but my guess is that arcade games have a lower cost per play in Japan - because there's more people to play them.
Here in the US, I've seen an arcade game in the wild run as much as $1.00/play, but I've seen the same title run as little as a quarter a play when in a high-traffic area (i.e.: Vegas hotel, shopping mall in super-large city, etc.).
If my game is going to be played 10 times a day vs. 50 times a day, then I'm going to have to charge more per play to make it worth the investment.