16x DVD writers getting more and more mature. Pioneer 110 and LG 4165 will have more features. Details are on Pioneer and LG forums. 1st gen. 16x DVD writers were rather awkward offering just a little faster speeds than 8x and 12x DVD writers and writing quality at 16x quite doubtful and supporting very few types of media at up to 16x full speed.
LG GSA-5163D is just an external version of GSA-4163B, nothing more, with USB 2.0 and IEEE 1394 and independent power supply. You can probably buy both Plextor 712A and LG 4163B for one GSA-5163D.
New ODDs at retail release time are usually priced lower than expected because of technological progress, volume of production, and competition.