Android System is what runs the phone. Turning it off is basically restarting the phone.
As far as the numbers you're seeing you interpreting them wrong. It's not that Android system is using 40-40% of the power abailable in the battery, it's that, of the power being used from the battery, android system is using about half of it. If you add up ll the other numbers you'll find out that 100% is being used. That's 100% of the power that's being used is being used. You'll ALWAYS have 100% of the power that's being used being used.
It's like you spend 20% of your expenditures on gas. That doesn't mean that you spend 20% of the money you earn on gas, it means that, of all the money you spend, 20% of it is being spend on gas. It may actually be very little money or it may be almost everything you earn, but that 20% (or 40-50% in the case of the phone( has nothing to do with how much is being spent or used, just with what percentge of the total amount being spent (or used) is spend (or used) on that item.
I'd rather see my phone use 90% of 1mA/hour on Android system than I would seeing it use 50% of 250mA/hour. In the first case it's using 0.5mA/hour, in the second case, with half the percentage, it's using 125mA/hour, or 250 times as much power.
Percentage of total and total amount are totally different things.
