Oh, that's weird, on both counts. My Corvette has what I would call a normally thin neck, as in, identical in thickness to that of other small-bodied 4-stringers such as my Bass Collection, for instance. The Fortress has a thin, comfortable neck, but my newer Warwicks (Corvette Pro 5 fretted and fretless) have an even thinner, shallower neck. It doesn't make a lot of difference when I'm playing, I must say.
The non-adjustable nut you have is almost certainly a replacement. All Warwicks have what they call their special "just-a-nut"; the cheapo models have it in plastic, the expensive ones in brass. I hate having to do without one on my non-Warwick basses.