Newer models don't always mean "upgrades." When manufacturers introduce newer models, they do it for adding features, reducing manufacturing cost, fixing bugs, etc. LG once switched from 8MB buffer to 2MB buffer, Japanese chipsets to Mediatek (Taiwanese) chipsets, Made in Korea to Made in China, Easy CD Creator to Nero Burning ROM, etc. and not all of such decisions were made for improving performance and quality but to save cost. Latest LG DVD writers also have simpler and smaller PCBs. And no DVD-RAM bundle media.
My guess is that GSA-4167B specification was finalized before 8x DVD+R DL was finalized and approved and so LG had not enough time to add it. Same with 16x DVD-RAM.
NEC has so far introduced three 16x DVD burner series:
Pioneer: DVR-A08, DVR-A09, DVR-A10
Hitachi-LG: GSA-4160B, GSA-4163B, GSA-4167B
Philips-BenQ: DW1600, DW1620, DW1620 Pro, DW1640
Toshiba-Samsung: TS-H552A, TS-H552B, TS-H552U, TS-H552C
Sony and Lite-On: SOHW-1613S, SOHW-1633S, SOHW-1653S, SOHW-1673S, SOHW-1693S, and more coming sooner or later
There were always small added features, small improvement between product generations if any. If LG had to "skip" GSA-4167B, then what about Lite-On and BenQ? I personally once had a few SOHW-1213S (but running 1613S or 1633S fw), and SIX SOHW-1613S, all outdated for long and now four 1613S and six DW1620.
Here are what are added in GSA-4167B from GSA-4163B:
[B]1. 4x DVD+R DL to 6x DVD+R DL
No DVD-R DL to 4x DVD-R DL
40x CD-R to 48x CD-R
24x CD-RW to 32x CD-RW[/B]
I don't think they are improvements that can't justify their existence as new products considering they (all mentioned in this post) are all 16x DVD writers and GSA-4167B price at first market release is much lower than that of GSA-4163B three quarters (late 2004) ago.