According to Tim Rogers[1] in-app purchases are already being regulated in Japan. As far as I understand it there must be a finite number of purchases, leading to a "maximum spend" per title, which can be shown in-store.

Not sure how this ties in with that, but it seems several companies are also self-regulating by imposing a spending-limit based on the customers age[2].

[1] https://twitter.com/108/status/292004594555449345

[2] http://www.gamasutra.com/view/news/169254/report_social_gami...