Yes, there is a difference - it :not(:disabled)can correspond to elements that are not :enabledand :disabled. These are elements in which the enabling / disabling semantics simply not applicable, e.g. div, p, uletc.
spec confirms this:
, , . :enabled, :disabled.
, :checked - :unchecked, , / . . .
(, input, select textarea) , , , . , :enabled, :not(:disabled).
3 - , :enabled :disabled. , MDN, Opera 9.0 Safari 3.1 :not(), :enabled :disabled , - sibling ~ IE7 IE8.