Hi jermmd.
The purpose of the aluminum plate is to allow a cutout in the back of the speaker cabinet for ease of access in mounting standard length binding posts. Jim can mount the posts on the plate, attach the wires to the posts while still outside the speaker, and then attach the post/plate assembly to the speaker. If you wanted to mount standard length posts directly to the veneer covered 3/4" MDF surface that forms the back of the speaker, there would not be enough post extending into the speaker interior for Jim to attach the speaker wire. If you select a binding post assembly that provides longer posts, however, Jim can mount them directly to the veneered surface without a plate at all. (I suspect that it still isn't easy for Jim, however, since while the extra length makes wire attachment possible, he is now forced to work within the cabinet through the woofer hole instead of externally.)
I was forced to go this route with my HT3s since I will have my crossovers mounted in external enclosures. This means that I will have 3 pairs of binding posts on the speaker cabinet itself. Jim has no plates that accomodate 3 pairs of posts, and I didn't like the idea of a double plate and single plate. The answer was to use Cardas Patented Binding Posts with the long copper post option. You might want to consider this option as well. For reference, there is another long post option for the CPBP, which I think uses Rhodium plating or similar. I will have the posts on my external crossover enclosures mounted in the same fashion, even though the walls of the external enclosure are thinner than that of the main cabinet.
(It sounds like my pair of HT3s is sharing an almost identical time schedule with yours, all the way from ordering to finishing. I suspect that my cabinets are finished, but the external crossover enclosures are probably still under construction or in some stage of finishing. The wait is painful indeed!)