Should Artists' only do one Medium?

I have been told that one only becomes a....." good well known Artist" is if they do only one medium.
However, I found that is not the case at all. Here are a couple of examples. Biggies to be sure.

Michelangelo di Lodovico Buonarroti Simoni
He was well know for doing ..
sculpture, painting, architecture and poetry
Explore his world
http://www.wga.hu/frames-e.html?/html/l/leonardo/

Leonardo di ser Piero da Vinci
Well known for all his endeavors of..
Math, engineer, inventor, anatomist, sculptor, architect, writer and so on..also considered one of the most famous painters of his time.
Some of his Art can be seen here.
http://www.wga.hu/frames-e.html?/html/l/leonardo/

So my words of wisdom to anyone either, just starting out, master Artist or inbetween...
Explore and create to your hearts content, be willing to spread your own wings and follow your Art where ever it may go.
Don't worry about what other's say you should or should not do.
Only you know what interests you, even if it is many mediums instead of one or any combination there of.
In doing this, you will find that you will complete your best works.