Correct (volatility). Nikkei has a fat, trending nature. Compare to YM (which is by far my favorite US trading instrument).
Nikkei is at roughly 16k. Many days it will have several swings from 50 to 150 pts at a time.
Compare that to YM, which is at roughly 11k, and the relative swing sizes (intraday).
I don't like the spread on Nikkei (i trade the futures through Singapore), which is 5 pts, but i try to use it to my advantage, by buying the bid and selling the ask.