Problem is that the AA batteries are more reliable because if I forget to bring them or if they run low, picking up another set of freshly recharged batteries or brand-new alkalines is a snap.
The camera with a lithium ion battery pack is more often a brick than it is a camera, in my humble experience - due to battery pack problems. I never buy any lithium ion camera or any other device (telephone, miniature tv, etc.,) if it exists with AA batteries.
AA batteries, in the long run, are vastly more "reliable" than any other type of battery pack (when you include the down time when you don't have a spare battery or a spare charger available).