ASK!
Apple stores, like O2 stores should have some way of easily checking the total stock levels at a company wide and also a store by store level for the different SKU - i.e. the 8GB black, 167 GB black and the 16GB white. If you are nice, and they are friendly, you'll get the answer you need in a day or two, whenever tehe stock registers into the system, prior to Friday.
Would Apple keep the White 16GB exclusive to Apple stores at the start? Who knows. Maybe they want to bring a certain demographic into the Apple stores. Lack of availability sure will increase perceived image.