I know but the car speaker is very different than a high detail Hi-Fi. You can never know, maybe in the future you will obtain such a system, and then the mp3 will show its weekness. It is a compressed format, and on speakers that are meant to project with much detail, segments will be missing from the spectrum, and you will hear it. It doesn't have to do anything with how serious you are about the quality of recordings, it is pure physics. Mp3 is meant for lower detail systems, like Hi-Fi mini towers, pc speakers, portable players and car.
However If you purchase from iTunes, maybe they offer lossless format, I am not sure. I rarely purchase digitally.