A rep from Paxum is here on the forums. He says they have rigorous verification processes that make fraud very unlikely. So, they don't have losses that they need to pawn off on their customers.
Dwolla was pretty much just on the honor system, apparently. Which is odd. I got a phone call from Dwolla when I set up my account, just to verify my info. I still haven't added any banking info to my dwolla account.
I didn't see under what conditions Paxum can reverse charges. They should mention that. Mr. Paxum are you listening?
Certainly if someone compromises the bank or Paxum account, I suspect Paxum will block, maybe reverse transactions. While perhaps unlike, what are the circumstances and procedures?