besides my own personal experiences with bikes for most of my life, here are a few examples from a noted bike guru who's actually put in real effort to study bearings and other unimportant, trivial things like that...
from Jobst Brandt
http://www.sheldonbrown.com/brandt/:
"The bearings of which we speak in bicycles are primarily cup and cone
bearings in which the cage serves merely as a convenience for
assembly. It has no function other than that. Cheap bearings, that
we needn't consider, often use cages to reduce the number of balls,
cages being cheaper than balls."
"Ball bearing failure occurs primarily through subsurface fatigue that
results in spalling, the flaking of the ball surface. Especially at
the speeds of bicycle use, surface speeds and frictional wear are
insignificant. The two modes of failure in bicycles are spalling and
contamination with dirt and water. Neither of these are affected by
balls making contact with one another."
here's some other stuff written by him if you're bored:
http://yarchive.net/bike/index.html