Well, older models had that problem with the square button (something to do with the actual "trigger" not being right under the button itself, since it was so close to the screen). Other than that it's just a bit more sensitive to damage than the DS, largely because of the use of a disc system. Usually it's durable enough to withstand normal wear and tear, but there are odd units in anything that's mass-produced.
Yeah, the system DOES seem like it'd be easier to break.
I've held one of the newer ones though. It seems MUCH sturdier.