Hey there mstation,
I've explained in a more simple way what each WD drive from the consumer line generally is here: http://linustechtips.com/main/topic/291871-wd-question-thread-hard-drives-dual-drive-setups-storage-setup-optimization/page-5
Although differences can't be noticed at first glance, the firmware of each drive differs from the others to suit the purpose of the drive. Speed and noise is not everything that makes a drive good or bad for a certain type of usage. These changes and features in the drive's hardware and firmware make it better either for an extensive high workload in a more hostile environment, or perform more stable in a case with more drives that work very closely to each other 24/7, or saves energy and has a much lower noise levels, or has its sequential read or write speeds much more improved in expense for the random ones, or has an improved or changed caching system, or something else. This is why each drive is recommended for different reasons and has its own design.
Feel free to ask if aI can help with something else
Captain_WD.
