The /proc/cpuinfo just tells you if it's available or not, not if the bit is enabled. Most 32-bit variants of Linux runs without PAE enabled, and without PAE enabled, all bits of the page-table are used. In PAE-mode, the page-table entries are 64-bit long, and the highest bit (bit 63) is used to indicate "NX" enabled or not (along with a bit in CR4 to enable NX).
--
Mats