Make your Mark and cutie marks...

[wonko the sane?]

So... why the hell are they only on the one side? Aren't the stamps supposed to be on both sides of the plot?

 

[ZakuConvoy]

I want to say because of the toys. So they can save just a *little* bit of money on paint. Also, there seem to be a gimmick this generation where you can plug in a "accessory" on the other side of the pony's flank.

In universe? Eh...let's blame it on Twilight.