When purchasing new tires, do you really need all 4 tires the same wear?

Generally no. I've never bothered to rotate tires, so the front ones on my FWD cars wear out faster. This has never caused a problem with the ABS / traction control systems, or the way the car handles.

OK, in a prefect world you should rotate your tires, so they all wear down about the same time. Then replace all 4 with a new set. But in the real world, you don't HAVE to.

It is always best to replace tires in pairs, if not the entire set. All tires should be not only the size size but they should also have the same speed and load index rating. Ideally they will be the same brand and model of tire but that is not absolutely necessary if the size, speed and load index ratings match.

Only on a vehicle that has symmetrical all-wheel-drive, such as a Subaru. In most cases, it is best to replace both front or both back at once, but with a 2 wheel drive car, you can usually get by with just one at a time.

No but tires on the same axle need to be the same

If the vehicle is AWD yes they do need to be the same amount of wear.

That depends.