This is a topic that is often raised but i admit i cannot recall all the answer but i know hard drive formating is a science in its own right, i think there is a link to the goodells web site that goes into mind boggling detail, another post does reference it ,try a search of the forum. I do not think XP does see the hidden stuff for a start and byte calculation accounts for the rest i.e. is a kb 1000 or 1024 bytes.
Anyway i am sure these drives are not some "seconds". Seagate would not allow them out the factory gate and Dell would not want them. Drives are now such cheap items it is not worth either of them doing such a thing.
Just and FYI, i have three of these drives for 5 years, 2 are still perfect, and one has 2 reallocated sectors now for 2 years.
They've been great drives, no complaints.