Heh. Just working with different concepts, I guess.
I've always pictured the HHH as a magical version of the USArmy's rucksack/backpack, though it's apparently closer to the silly things I've been mentally calling one-strap backpacks that I've seen a lot of adolescent girls carry here in the DC Metro area.
The reason for that is that it's described as having multiple pockets on the outside. And the haversacks(?) I've seen the girls carrying are definitely worn on the back, and thus out of reach. In fact, if the haversack was worn like a purse, the openings would point towards the ground, not up. Much harder to access than a purse.
On the other hand, there's *ample* real-world justification for "purses of holding", I've just never pictured the HHH as such.
As for the extra-dimensional thing, I've always treated the exterior container as being the walls of the interior; any gross changes (like wringing a bag of holding like a towel, or stepping on a HHH) apply to the interior (and thus its contents) as well. In other words, they don't protect the contents any more than a normal container would, they just allow you to carry more.
Of course, I also return the contents to the game world instead of having them be permanently lost (under most conditions).
Shrug. It's never really been an issue in my games.
---- Edit -----
From the DMG:
Heward's Handy Haversack: A backpack of this sort....{snip}....and whatever it contains gain a +2 resistance bonus to all saving throws.
At least I'm not the only one to make those "mistakes".