All weapons have Blunt DRs because it is a fantasy myth (fantasy in the bad sense of crazy and idiotic) that any hand-held weapon is ever able to actually cut through armour-grade metal. Punch a tiny hole in it certainly, make a tiny, half-inch tear in it maybe, but actually cut it no way. Any cutting weapon hitting metal armour will therefore damage its wearer only via blunt trauma transmitted through the armour, without actually penetrating the armour in any way that matters. An axe blow to your helmet will never ever cleave your skull, but it will give you a nasty concussion, possibly knock youcold out, maybe even break your neck. And that’s why the axe has a Blunt DR, to use in these cases. As does every other weapon.
The rules for this are on page 151, btw.
Weapons that very obviously don’t have either Piercing or Cleaving damage don’t state that the damage they cause is Blunt, because we think that rather obvious. A club does very clearly neither slice nor prick, it causes blunt trauma. That’s so obvious that it doesn’t need to be spelled out.
What threw you off track is that you forgot that you cannot only whack somebody with a club, you can also jab with it. One’s a Swing, the other a Thrust. Both are very different actions, using different ATNs and having different DRs, but both of them still Blunt. Of course, you wouldn’t normally jab with a club, but there can be quite a few instances when jabbing with it is the better choice, so we give you the stats for it.
All clear?
