@gaspower: I think it must depend on the quality of the battery as well, because I've had one of my dualshocks for 4 years and it still works fine, but the rechargeable pack in my 360 controller stopped working after about 4 months.
That's true as well as a lot of other variables too such as the temperature of the storage area. I'd rather be able to just replace the batteries instead of choosing the more expensive option of outright buying another controller when given the option, right?
Well I like to replace my controller every few years once the buttons get worn down anyways. But I suppose it's good to have the option of replaceable batteries.