Agree, this must be trolling... Grant it, I think that at some point, varying the number of party members would be awesome, but there would need to be extra balancing involved. Such as increasing the number of monsters, or buffing them if you have over 4 party members. Then debuffing or decreasing the number of enemies if less than 4. DoS2 had 2 mods for this to balance the difficulty.
And just for the record, the 4 person party concept started with Final Fantasy, way back in 1987. :P