It has been a while since anyone has contributed to this thread, but after some searching, I found that the use of more has no bearing on whether it is countable or not.
e.g.
There are more apples than oranges
There is more water than juice
Greater seems to refer to being "Larger in size or importance or degree."
Hence, we can say the following:
The number of apples is greater than the number of oranges
The amount of water is greater than the amount of juice
The clarity of water is greater than that of juice
The fraction of the population who smoke is greater than those who do not [smoke]
In these examples, less could could be substituted as an adverb not as an adjective, which I think is what is creating the confusion.
Comments?