pet peeve - odd shape cards

Today I walked to walgreens to buy my cousin a birthday card. I searched and searched for just the right card and I got out of there empty handed. The fun cards I wanted to buy are square and I do not really know how much postage to use for it. Odd shaped envelops require extra postage. If I got that square card, I would have to make a trip to the post office which I simply do not have the time due to work. I just like to be able to stick a postage on it and drop it in the mail box. And the regular rectangle cards they have are lame.

So why do they have to make square cards? What on earth would a square card serve that a rectangle card can not accomplish? Seriously, it bewilders me.