J2ME is already used on a lot of mobile phones.
From a high level view, yes this is the case, dig a little deeper and you'd see that there are multiple versions needed for the vast amount of devices.
When I left 3+ years ago we did like 45 different groups of devices.
Maybe using Sun's J2ME commercially is too much expensive, this would explain why Google created the Dalvik VM.
More like each vendor had their own ideas about realizing J2ME on their phones and Google is just the next one.
Anyway, it is difficult to use Java for commercial games except on computers and mobile phones (excluding IPhone).
Java on mobile is a PITA. Very far from the write once/run everywhere concept.
If you want to sell your games, you need a LOT of portals (kinda like a publisher) to provide your games to the masses.
Not to mention the price ranges and margins available.