mp3 is a compressd file format, when you change a .wav file into a .mp3 the algorithm starts throwing out ''non essential'' frequencies, this results in a smaller file format, handy for chucking a whole bunch of music onto one carrier (carrier as in mp3 player, ipod etc) but will dramaticaly decrease the dynamic nature of a track, this effect causes people to say the ''audio quality is less than...''
the fact that on (most clearly visible) the mid/left picture you haven't got a nice and round sinewave but more of an edgy one is possibly due to a low sample rate, for more detailed info on that, go here >
http://en.wikipedia.org/wiki/Sampling_rate
hope this helps
