The difference between low-res and high-res MP3s is the bit rate at which they're sampled. Our low-res MP3 masters are sampled at 192 kilobits per second, and our high-res MP3 masters are sampled at 320 kilobits per second. If there are more kilobits per second, there is more audio information, making the master higher quality.
Uncompressed WAV format is a totally different file format than an MP3, because it is lossless.
Lossless audio formats keep all of the original source audio information, so they are of a much higher resolution and quality.