Well, lots of characters doesn't automatically mean "good game". Besides, who ever plays as Dodoria or #19 in the Budokai games? (And I know that some smart arse is going to pop up now saying that Dodoria is his favourite character. But the person who does that is quite obviously a fool).
I'm assuming that the lack of characters is more due to cart space than anything. And if you had to pick 6 characters, those 6 do make the most sense (as much as I would have liked Kuririn to be in there).
And at least they aren't doing the old PS1 game trick of having 5 different versions of Goku all be "different characters".
(LATE ADDITION)
Looking over the whole site, I'd say that the game will have more than 6 characters. Look on
this page, at the bottom left picture. That's pretty obviously a character selection screen. A character selection screen with lots and lots of question mark slots. They have to be unlockable characters, which are...completely expected from a Japanese game.