Hi Daryl,
I've heard both: that they are slimmer, and that they are not slimmer in a consistent way.
In other words some of the necks did "feel" like it because of the vagaries of hand-tooling each neck. Clearly with the advent of CNC on the NT necks, consistency is in the thou-of-inches. so every neck felt identical. I buy this second reason: that if each neck were rough-machine shaped then hand sanded, there could easily be noticible differences. But a consistently thinner neck on all guitars pre-NT? That I am unsure of (never owned an pre-NT).
That said, even with their so-called "slim carve" neck (that I have heard is supposed to emulate the "old feel"), I can barely tell a difference; and if I can it'd be only if I were looking for it. Casually picking up a "regular" NT and a "slim carve NT" doesn't raise any glaring differences in my hands that gives me any pause ...for me anywho.
Edward