Sales per capita: Major European countries > Japan. Japan > Europe.
Sales per country: Japan > Biggest individual European country.
Sales per region: Europe >>> Japan.
The obvious reason Europe is more important than Japan is because the individual European countries are largely interconnected and share similar tastes in gaming and entertainment in general. Unlike Japan, which is its own tiny strange world that not many people can relate themsleves to. A major game that targets the average English gamer will also cater to Germans, Italians etc, and to a less extent Americans and pretty much every economically healthy-ish place in the world that isn't East Asia. A game that is designed for the Japanese will sell terribly outside Japan, barring a few Nintendo titles, and even fewer third party titles. This doesn't help or encourage Japanese publishers to spend much into the making and marketing of their games. Most publishers avoid taking risks for very understandable reasons.