Well, for me, I'm surprised that the card slots are so reliable. How many people find 'gunk*' in their slots that renders it unusable?
Heck, my 5 lived in an OtterBox for its entire life, and I was still amazed at the 'gunk*' that built-up in the front speaker slot, and the bottom speaker holes.
People that carry their slot equipped devices must have so much crap in the slots over time that I'd imagine they get too stuffed with it. I've seen micro-USB ports that look communicable. It's hard to tell what's living in the thin crevices, but it doesn't look benign...
* - Gunk, see 'life happens': dust, dirt, sweat, moisture, sand, hair, etc...