As I view it, Natural 1s miss on attacks because you're trying to attack something that is actively avoiding trying to be hit, yet has a static AC. Whereas skill checks are against static things that can't fight back (lock, recalling lore, tightrope) or are contested checks. For the later, the "contested" part allows for the enemy to roll high and succeed at, e.g., dodging a grapple against an expert grappler. Similarly, a Nat 1 on an attack roll represents the (possibly unlikely) chance your opponent successfully dodges/blocks your blow.
For the same reason, I think Nat 1s and 20s should be autofails/successes for Saving Throws. You're rolling against a static DC, but you're actively trying to avoid an effect created by someone else, so it's actually a contest.
