It's actually only $2 ($1 each) or so for the Bumpers... the remaining $56 (or the $28 off the individual price) is because you're paying for Apple magical rubber... it's not like ordinary rubber, of course.
I'm sure someone has said this, but has Apple ever made an iPhone case before? I don't think they have. I'd bet a years salary that these bumpers exist solely because Apple knew about the antenna issue. The engineer they hired back in January warned them but it was too late to make a change. And then the bumper was born.
Bumpers are way over priced. For $25 you can get a proper case that will protect the back from scratches, and you will have a bigger chance of your iPhone surviving when it gets dropped on the ground.
Not to disagree with you...we all use and handle our phones differently...but for me...the bumper provides more than adequate protect for the back of the iPhone if set down face up. So that's all I need. I don't need the added bulk of a full sleeve.
Unless you drop the phone so the back hits a corner of a table at an angle or similarly...I don't think a full back will provide any better protection. In most cases (99% of the time I would guess) when you drop the phone it will land on one of the sides or a corner. The bumper provides protection for this.