This is not an answer (I asked the question, LOL) but follow-ups to the questions asked by the people who have kindly answered my question:
1. I do have low-profile tires. I think the profile ratio is 50%, and the wheel diameter is 16 inches. The car originally came with these low-profile tires, and I have been using the same size of tires ever since I bought the car.
2. I do not remember the exact event, although I suspect that my skidding off a slippery, icy road late last year might be the culprit.
The roads I have used in the past 2 years have hardly had potholes, so I don't think potholes are the culprit.
3. According to the link kindly provided by Mr. Shiftright, the cost of repairing a bent wheel ($75) is not much less than the price of a new aftermarket wheel (from $83 to about $110 at Discount Tire). New OEM wheels cost a ridiculous $500 a piece, so replacement with new OEM wheels is not an option. It might be a good idea to just replace my OEM wheels with aftermarket ones, assuming that the aftermarket wheels are at least of the same quality as the OEM ones.