Sony has clarified that, although four of the Move wand controllers can be used at a time, the PS3 motion control system only supports two Move controllers and two of the offhand "sub-controllers" at once.
There's a cap of four controllers total, explained Justin Cooney, a senior account manager for developer support at Sony Computer Entertainment America, in a GDC session.
That includes the nunchuck-style wireless offhand controllers. "I always think of it as the left side of a Sixaxis," Cooney said,
Although Cooney didn't discuss details, the restriction is likely due to the fact the Move sub-controller uses Bluetooth to connect wirelessly and independently with the PS3.
This is unlike Nintendo's system, whereby the wired nunchuck sends information back over the same wireless connection as the Wii remote.
Sony is about to make its main presentation of the Move to developers at GDC - we'll let you know if there are further details.