On the A/C, you should recharge every 5-10 years regardless of mileage (basically as soon as the A/C starts getting noticeably less cold), not wait until it doesn't work anymore.
A refrigerator doesn't leak it's refrigerant (unless it's rusted out) because it uses an entirely metal system. In a car where the A/C is belt-driven, they have to use rubber hoses between the evaporator and compressor because the engine flexes around. The refrigerant actually seeps through the microscopic pores in the rubber over time. Once pressure is reduced enough, the compressor will work harder and wear itself out much faster, and with less refrigerant in the system eventually the rubber joints/gaskets will dry out and crack (and not hold any pressure if you do recharge it). The lower pressure can also let moisture in, which can rust out the compressor.
This is also another reason to run the A/C periodically (even in winter, run it with higher temperature setting with the defrost) to keep everything circulating and avoid gaskets drying out and the compressor freezing in place.
I went through something similar to what you did with an old 1992 Ford Exploder (misspelling intended, it had so many problems it should have been returned under the lemon law by the first owner). I didn't do anything to the A/C for months after it stopped working, then had various parts replaced twice, and it still wouldn't hold refrigerant more than 3-4 weeks. That was a money hole.
The A/C in my current vehicle was getting much less cold and taking longer to cool down (8 years since last serviced). I thought it might be a goner but I had it tested and recharged, and it's been holding strong for a couple months.
