Just to be clear for anyone who's unsure, WotC-D&D does not assume all creatures are square (or round, I suppose, if you look at the mini bases). It's that WotC-D&D does not consider facing in its combat rules, so there is no meaning to 'front' or 'side' to a creature in combat. A creature that's longer than it is wide therefore cannot be represented that way on the battle grid, since that would require knowledge of which direction the creature is facing. It's the same type of thing that Small creatures take up as much space as Medium ones - how can a halfling possibly fill 25 square feet just by standing there? He can't; it's an abstraction.
You might not like this, but your choice to characterize the decision as "they think all creatures are square" is presumably what got Dire Bare involved. There are less misleading ways of making your point.