The two rules certainly seem to be inconsistent, but why do you think the non-endzone fumble out of bounds rule is preferable to the endzone fumble out of bounds rule?
The endzone fumble out of bounds rule actually makes more sense than allowing an offense to retain the ball when fumbling out of bounds in the non-endzone area of the field, does it not? It rewards the defense and punishes the offense when neither is able to recover the ball within the field of play. A fumble is a free ball, why punish the defense when it is not recovered in the field of play by either team? It is the offense that made a mistake.
Haven't really thought this through, but upon first glance, those are my thoughts.