There are actually Lithium-Ion in AA size, but they're actually called 14500. They have a nominal voltage of 3.7, which means they're about 4.2V when fully charged. This makes them unsuitable for directly replacing alkaline and nimh in most devices, though if you have a device that takes 2 or 3 AA, you can use 1 14500 Lithium-Ion rechargeable and 1 or 2 dummy cells. Not much sense in doing that, you'll have more energy in 2 AA eneloop.
Safety is probably the main reason why we aren't seeing standardized sizes for Lithium rechargeables used. Considering that consumers today already ignore the warnings on alkaline and nimh batteries, putting Lithium-ion in their hands would be disastrous. While nimh or alkaline at most leaks a bit of corrosive electrolyte, lithiums "vent with flame" when mistreated... The situation is not made easier by the fact that there are about half a dozen different lithium-ion rechargeable chemistries, each preferring a slightly different charge algorithm. If consumers have more than two kinds of lithium and use the wrong charger, they might find a new fountain of flame in their living room.
That a nimh battery's label says "1300mAh, Charge 130mA 14 hours" is entirely correct. When charging at a rate that is one tenth of the battery's rated capacity, the charge efficiency is somewhere roughly around 70%, meaning that you have to put in 1.4 times the battery's capacity in order to fill it up. The "missing" 40% warms up the battery.
Regarding the cost of electricity, if we assume you treat your battery well and will thus get about 500 cycles out of it, you'll have put in 500 cycles * 1.2volts * 2AmpHours * 1.4 (charge efficiency losses) = 1680 watthours of energy. That's 1.68 kWh. Assume that the charger and its AC adapter are somewhat inefficient, say a very pessimistic 50% efficiency 3.36 kWh. A kWh costs less than 50 cents in most parts of the world, but let's assume you're paying 50 cents, round it up, about $2 in electricity costs to charge a Eneloop AA battery 500 times. This is why people rarely factor in the electricity cost, even with this pessimistic calculation it is insignificant. How much does 500 AA alkalines cost?
Btw, to those of you who have the "null" problem with the BC-900, do keep in mind that it's generally a bad idea to drain nimh completely empty. Cameras and such shut down long before the batteries are empty, but less "high tech" devices such as flashlights can be run past the point where it goes dim. If the flashlight uses more than one battery, it is likely that one of the batteries will go empty before the other, this results in the remaining battery "reverse charging" the empty battery. This is quite harmful for a nimh battery, and will greatly decrease its lifetime. nimh batteries also don't like to wait around in a discharged state for very long, so charge as soon as possible, and it's okay, even recommended, to recharge the batteries as soon as you notice the flashlight dimming. The old urban legend about running flashlight until it's completely dead in order to maximize rechargeable performance is wrong.
Many people use the term "memory effect" to describe all kinds of loss of performance, but the truth is that such a thing doesn't really exist in real life. The harsh reality of it is that batteries will die, and often it's a long and slow death. Lithium Ion rechargeables degrade and lose capacity (i.e. you get less and less talk time / laptop runtime even on full charge) over time. It used to be as high as 50% degradation in 2 years, hopefully research and progress has managed to improve this a bit. There's no memory effect involved, the battery just becomes weaker over time. Completely discharging Li-Ion wont magically make it perform better, it's even outright dangerous to use a Li-Ion that has been discharged past the point where the device no longer operates on it.
So many issues, still so many rumours and false tips floating around about "memory" and similar, it's no wonder people just find it simpler to continue throwing money into the alkaline pit..