Ordinarily one would think so. However, I have purchased 6 of the Maxtor DM+9 200 GB model, mfg. from late 2002 (IIRC) to September 2003. They are all 6 head drives, although 80 GB/platter 250 GB drives have been available for more than 6 months. I don't know if it is not worth the mfg. costs to produce a 5 head design, or the heads and platters for 66 GB/platter are cheaper, or heads and/or platters are binned depending on yileds, or what. Perhaps Mickey can shed some light on this. Regardless, the platter density issue has been beaten to death, and the difference between a 66 GB/platter and a 83 GB/platter drive is negligible.
There are a goodly number of retail packaged drives that may not exist on the manufacturer's webite. For example the 300 GB DM 16 was sold at retail stores throughout the U.S. in retail Maxtor packaging although is was not listed on the website for months.