@Lithium I don't think anyone is suggesting eschewing dice in favor of something else, as, yeah, the code for the rolls is right there and there's no reason to not use it.
It's more a factor of how much is left vague and up to GM judgment calls.
Here's how numbers factor in here:
- Larger group of players == need for more than one GM.
- Need for more than one GM == need for guidelines to keep judgment calls consistent amongst GMs.
A lot of systems, by default, assume there's only going to be one GM for the game. Shifting from one to multiple GMs, by necessity, means a lot of the deliberately vague 'up to the GM/ST' situations in the books are going to need at least some clarification or additional guidelines to keep a measure of consistency. (WoD/CoD, I am looking real hard at you here; other systems are more clear, it varies a lot, but the problem is universal with that shift in who is running what.)
If you're creating the system from scratch, minimizing the instances of 'the results are up to the ST' judgment calls also means players can handle more things on their own without the need for ST oversight (which is not always available and/or timely in our medium). The more players you have, the more that autonomy becomes important. The ability those players have to be able to reliably handle the outcome of a roll or power without the need for additional oversight or interpretation to get the results allows them to do more with less top-down guidance, and that's a critical tool for players that's often overlooked in tabletop game design -- since it's not relevant at the table; play stops and starts when the GM/ST starts the game and they're typically present throughout. MUX/MUSH/etc. has 24 hour game play. Heavily coded games take this into account by having the code handle it, but in the same way, a system with clearer, more defined outcomes and result parameters can be a huge help without the need for heavy code.