............The in-body focusing motor is a nod to users who have money invested in "old" AF lenses, dating back to the mid-1980's............
But why put focus motors in lenses the entry-level users are NEVER going to buy? Seriously.... how many D40 and D60 users are gonna pony up $9k for a 500mm prime? The target market for long glass is those who own bodies with focus motors in them already.
Are you seriously asking why put high-performance, specifically-dedicated, lens-appropriate, silent-wave coreless focusing motors in lenses designed to offer fast,accurate,silent focusing? You know, focusing motors that have been engineered, and tested, and SPECIFICALLY optimized for each,specific lens design? Are you aware of the difference in how a dedicated, AF-S motor can predict focus and arrive at a precise focus spot in ONE, single,discrete movement, as opposed to a series of check-compare-check-compare-check-compare hit-and miss estimations, and minor corrections that screw-driven, "universal" focusing is plagued by?
In-LENS coreless focusing motors are the silent, fast, reliable way to achieve almost instant focusing, as well as to achieve follow-focus, and predictive autofocus. In-LENS AF motors mean that each lens has its own focusing motor that is carefully designed to handle the needs of that one, specific lens design; if the focusing group is small, a smaller motor can be used. If the focusing group is large, a larger, beefier motor can be used. In ALL ways, every single camera maker has decided that the "best" system for AF lenses is in-LENS focusing motors of the silent-wave type.
In-LENS focusing motors have made a huge improvement in the focusing performance of ALL lens types!!! A 300 f/2.8 with a screw-drive system sucks. A 300/2.8 with a Nikon AF-S motor is a dream. A 35-70mm f/3.3~4.5 AF Nikkor goes dzzzt!dzzzt!dzzzzt! back and forth,m back and forth, as it tries to screw-driver focus in dim light...the 24-85 AF-S goes "dit", and in .3 second is LOCKED on..............and both are cheaper, low-spec lenses...
In-lens focusing motors are the best way to focus modern AF lenses. That's just a fact of how screw-drive works, as opposed to silent wave...on slow f/4.5~5.6 type lenses, silent wave motors offer vastly better focusing performance than screw-drive ever did. THe reason is that EACH lens can be driven to a *specific*,discrete focusing distance based on the data; screw-driver focusing works on the basis of continually checking the status of the focus with NO feedback, no predictive transfer of information....
screw drive focusing is based on trial and error, trial and error, all done fairly rapidly. AF-S protocol is specific, to each lens's focal length and aperture, and has predictive capability, and so it can actually collect the initial data, and drive the lens to a single,discrete,specific,exact, precise distance, in ONE, single movement. Silently. And fast. Over and over and over and over again. Even with slow-aperture lenses. One is building with a set of blueprints (AF-S, HSM). The other is building as you go, scrounging bits and trimming mistakes and fixing boo-boos continually until the job is finally done (screw-drive).