Microphones have different characteristics, as does every other piece of gear.  That is why some people think an SM-58 (for example) is the best mic in the world, while other people sound and do better with something else. 

Some people also just have voices that sound better when recorded than others.  Some radio DJs, even back in the old days before assorted enhancements, had what was called the VoG or "Voice of God" where they just sounded great on the air.

Violins are complex instruments with rich harmonic content, so it stands to reason some might sound better with a certain mic (or other gear in the audio chain to the recorder) than others.

Also some performers can, by instinct or luck or training, get more "pizazz" out of a recording session than others who may sound fine in person.  It can be due to a lot of factors, but envelope and harmonic content are usually the most obvious causes.

Also you have to consider that while a microphone "hears" only a single spot of sound, the vibrational sound field of a violin is a complex 3 dimensional thing that shifts with every little move the player makes.  It doesn't just emit sound from the top, but some also through the back and directly from the strings, and so on.  That is before you even consider reflections of the sound off walls and floor, which also constantly shift because the player moves the instrument when playing.  This is one of the reasons it is considered notoriously difficult to mic a violin and really get a great result.  A grand piano, for example, is also complex so far as sound field, but it doesn't move when it is played.

Sorry for the "tech geek" answer, but one of the questions on the final for a recording class I took in college years ago was something like "What is the most difficult orchestral instrument to mic properly for recording?  Explain."  ...and the correct answer was violin.