Thats not the case, WD always changes the last 5 digits of the full product number when the sku changes
the real problem is retailers and etailers tend to omit those numbers on product listings to keep the consumer in the dark.
tbh, WD's sku numbering is less complicated than seagates.
op, this site is tracking hdd platters, cache and capacity via sku numbering http://rml527.blogspot.com/2010/10/hdd-platter-database-western-digital-35.html