wavs having "more samples" is a new one to me. Neat.
WAVs support sampling rates up to 192khz, whereas mp3 only supports up to 48khz. However, you're unlikely to come across anything higher than 48khz anyway unless you specifically look for it, or record it yourself (as the author did).
Sampling rate has (basically) no effect on audio quality beyond the highest frequency the file can contain - you can drop the sampling rate right the way down to 8khz and it'll just sound a bit muffled but otherwise fine. The primary reason to prefer WAV files over MP3 is that encoding something to MP3 irreversibly mangles it, and the author would be justified in being extremely pissed off that Apple decided to unilaterally do this and delete the originals. It would be like deleting someone's RAW photos and providing Facebook-sized jpegs as replacement, or deleting their home movies and offering back gifs of them. Apple have committed a cardinal sin here, the seriousness of which can't really be overstated.