You're right about why Pass The Bomb isn't included [because everyone would be waiting for ages for their turn]. We had a test version of it built while making Quiz TV, and in eightplayer it took ages for the round to end. The other thing we found is that there were long gaps where some players were doing nothing, waiting for the bomb to come back around again. People just got a bit bored by the time it was over. Something similar is true of eightplayer Pie Fight - unless you give everyone just one life (pie hit) each, the round goes on for ages. And you can probably imagine that 'one hit and you're out' isn't much fun to play.
So in the end we decided to ship the rounds that gave the best possible experience in eight player mode - nothing more or less technical than that. And of course, you don't need to buy a set of wireless buzzers to play with 5-8 players - you can use a set of the PS2's wired ones instead, if you have some around.
Cheers,
Dan