"Serialism, as practiced by the big three, represented in part a rejection of harmonic variation and a renewed focus on counterpoint instead of harmony"

This is true, specially in Webern's compositions. The canonical (pun intended) example is Webern's Symphony op. 21, which is a four voice cannon:

http://www.youtube.com/watch?v=XKD_tZr-ZpY

Webern was greatly influenced by Renaissance composers such as Heinrich Isaac:

http://www.youtube.com/watch?v=zqpXLTJDsWg

On the other hand, Schoenberg and specifically Berg have a more harmonic approach to their compositions as we can see in Berg's violin concerto:

http://www.youtube.com/watch?v=oqSSHwFEn_8 http://en.wikipedia.org/wiki/Violin_Concerto_(Berg)