Ever since Apple started switching up the 802.11x and Bluetooth chipsets being used in Macs, it’s been unsure whether you need to get those options installed ahead of time. Considering most Mac models thus far have made both standard, it’s a thought that’s been put in the back of one’s mind.
Considering wireless is not part of the standard/default/suggested configuration of the Mac Pro, I was afraid you wouldn’t be able to get it done in the Apple Store. It’s officially confirmed that it can be done (Bluetooth and 802.11x individually). No reason to panic and buy unless you need it now.
802.11a support is also admitted in that document, as is the fact that Mac OS X doesn’t support it.
