Western Digital Model Differences (replaces Question From Yesterday)

Some sellers of Western Digital hard disks for laptops (250gb, often Dell laptops) sell model WD2500BJKT-75F4T0.  Others sell model WD2500BJKT, without the additional 75F4T0.  The plain WD2500BJKT is substantially less expensive, so there must be some difference between the two models.Similarly, the paragraph above applies also to the larger capacity (320gb) WD3200BJKT-75F4T0 (or -00F$T0) and WD3200BJKT models.Question:  What aew the differences in features or design between the 250gb WD2500BJKT-75F4T0 and WD2500BJKT, or the 320gb WD3200BJKT-75F4T0 (or -00F$T0) and WD3200BJKT?