My update MBP, core2duo running OSX 10.6.2 gives,
uname -a:
Darwin laptop.local 10.2.0 Darwin Kernel Version 10.2.0: Tue Nov 3 10:37:10 PST 2009; root:xnu-1486.2.11~1/RELEASE_I386 i386
uname -p:
i386
I guess they just use 'i386' and don't differentiate between 32 and 64 bit here...