Here is a page from Ed Roman's website about why ebony is so much "better" than rosewood:
http://www.edroman.com/customshop/wood/gaboon.htm
Here are a few reasons why he believes ebony is much better for fingerboards:
Benefits Of Using Ebony
1. Ebony is much harder and polishes up beautifully so that the neck feels smooth and slick. It's much harder and therefore you can get a better percussive tone when doing two hand tapping and hammer on's or playing without a pick.
2. Ebony reduces finger fatigue. If you play for hours your fingers will appreciate the smoothness. It's barely noticeable but the smoothness makes it so that you can play longer without getting sore fingers.
3. Cosmetically Beautiful, The Jet Black Ebony contrasts nicely with the binding and/or inlay material, also it effectively hides any filler for a much cleaner look.
4. Ebony is much stronger and much more stable. It helps keep your neck straighter and also protects it from breaking