Thanks DNH, as usual when it comes to maths I assume that if it looks almost right, it's close enough😛.
Regarding the flash drives, it may vary from manufacturer to manufacturer, some may use the 'true' mega/gigabyte storage capacities. Maybe it's the price of the OEM flash chips or the size that depends on how much space they have. Eg: my '512 meg' sony MS Duo only has about 470 megs.
One last thing: for extremely high end devices (ie SSD's and 10k+ rpm hard drives) manufacturers use the true values. ie the 64 gig SSD drive in the MBA actually is 64 gigs (64 * 1024 ^ 3 bytes).