My understanding was that gold was not counting as a player kill actually.
Oh, it definitely does (or at least very much appears to). From my recent testing (and for all I know maybe something was up with different versions or something) :
Wood Spikes will damage but not kill, leaving half a heart.
Iron Spikes count as player kills and mobs can drop rare items like heads and whatnot, but does not drop XP
Gold Spikes count as player kills and mobs drop XP
Diamond spikes don't appear to do anything more than Gold Spikes (except slightly more damage), but descriptions say that you can enchant them.
And I tried everything I could think of to enchant them because I really wanted to give it XP Boost, but only two useless mod enchants they would respond to, whether it be an anvil, the advanced enchanting table that lets you pick your enchants and the NEI enchantability page. And they were all the same from iron through diamond.
But, again, something may be broken on my end, or it could be a version bug or something.