My only guess is that the little antenna is tuned mostly for 800MHz and trunking performance, and that is what GRE went for.
Since you mentioned that, id say your most likely right on the antenna....We never had any 800 mhz here in my area, still dont. Im averaging 9 hrs with my eneloops,,i have my lcd at #4 and keypad turned off. I really like the sanyo's since ive used them past few yrs now, and id really like trying the newer black ones that are 2500 mah,,,but best average pricing ive seen on them is around $ 20. for pack of 4,,,I only paid $ 21.79 shipped for two packs of 4 of the white ones, that have the improved charge cycle life of up to 1500 charges now.