I wonder if Bust-a-Move and the like aren't achieving 8-player simultaneous by having one player use a nunchuck tethered to another player's remote. The system was designed for only four simultaneous players (look at the lights on the controller).
That didn't actually occur to me. Seems to be much easier and more plausible to use the accessories for players 5-8.
Not that it matters much for BaMB! It's already established that most light control on the WiiMote is done by the console, not by the controller itself. A developer could theoretically selectively light additional LED's beyond the typical 1,2,3,4 assignments. ie, player 5 could be LED's 1+4, 6 == 2+4, 7 == 3+4 and 8 could be 1+3+4 or whatever. That scheme doesn't exactly address usability issues though. I wouldn't want to play positions 5-8 because I wouldn't care to remember what light combination meant what.
Looks like you are correct. From gamespot:
The only clever thing about the versus mode, and perhaps Bust-A-Move Bash! on the whole, is the way you can have eight players on four sets of controllers by having one player use the Wii Remote while the other uses the Nunchuk or the Classic Controller. The Nunchuk doesn't work so great, but the Classic Controller is unsurprisingly the best way to play the game, which makes the inability to use it anywhere besides the versus mode supremely frustrating.
That's interesting. Not saying Gamespot is wrong but check out the
box art. When they pop that number on the WiiMote like that, isn't it supposed to denote the maximum number of simultaneous supported controllers? Not necessarily the maximum number of players? In fact, Nintendo explicitly defines what that symbol denotes
on their webpage:
Wii Remote:
The Wii Remote is the unique wireless controller for the Wii console. The following icon depicts how many Wii Remotes can be used at the same time during play (up to 4).
Oops.

Kind of a bummer really. I thought it was pretty cool that someone figured out how to break the 4 controller limit on the Wii.
Oh well.