from my tweets:
on DoCoMo: 2 days before Android handset launch, CEO Yamada reveals plans to setup own appstore for google/windows based smartphones as early as FY2010 (from interview on Fuji-Sankei Business-i).

Smartphone apps basically have two problems that halts significant growth here in Japan.
1) Quality un-insured, unstable.
Apps crash, stall and freeze,,, something that Japanese consumers who download apps onto their feature phones can't imagine happening (but are slowly gettting used too???).
2) Most app details and information not in Japanese
Users who download apps without understanding what's written in English are most likely early adopters. The general public expects app descriptions to be in Japanese so they can swift through the vast amount of offerings without making a wrong choice.

Not saying carrier control is optimum, but with them stepping in and insuring quality of the apps and promoting them in Japanese, would definitely act as a plus to the growth of not only app sales but eventually the handsets themselves.