I'm glad you have this kind of insider info the rest of us can only dream about!
I don't ever recall stating I have any inside info regarding the reasoning behind Weta's generic bases, but do you really need inside info to figure this out?
Do you really have to be a rocket scientist to figure out the time and costs incurred by Weta had they produced separate individual bases for each and every statue/character would have been significantly more had they gone that route? Not only would the additional R&D required, sculpting, mold production, and paint app costs have resulted in higher priced statues, they would have added significantly to the time required to produce them.....and based on the staggering rate at which Weta were producing these statues [close to one/month over a 5 year period] it is highly doubtful they could have accomplished this had they gone with anything other than generic mass-produced bases for the majority of their statues. And I don't think it a co-incidence that the only two Weta statue lines featuring mass-produced bases also happen to be the two largest they ever worked on...LOTR and Narnia. There's no doubt those generic bases are functional and served their purpose, but one thing is certain, they didn't produce those bases to visually or artistically enhance the statues. They produced them because they were cheap and easy to make, and it saved them alot of time and effort.
Now one might argue that great statues don't need intricate, detailed bases...that the character itself is enough. Personally, I do not think people who adhere to this belief could possibly be more 'off the mark'. Those like myself, who are avid collectors of artwork frame our litho's, canvas giclee's, etc...for two reasons. To protect the painting and to enhance the painting. The protection part I think is pretty self-explanatory. As for the enhancing aspect, again, it's pretty self-explanatory. Surrounding a picture with a proper frame/moulding and selecting mattes that compliment the picture or draw one's attention to certain aspects of that picture will make a great painting even better. As an avid fan and collector of Jerry Vanderstelt's LOTR painting's I can safely say that his artwork is stunning, but someone who doesn't think Jerry's amazing paintings can be improved upon by the careful selection of mouldings and mattes that compliment his artwork...doesn't know what they're talking about. And I would make the same arguement for statue bases. The statue that can't be improved upon by the careful selection of a base that compliments the overall statue doesn't exist. In all my years as a LOTR collector I have never once heard anyone complain about the bases of the SSW Balrog or Cave Troll statues. I've never heard a single person ever make the statement these statues would look as good, or better, on a plain, black, generic base. And the same goes with Bilbo standing on a barrel or Sauron standing on the lava encrusted landscape of Mordor. And the reason why you never hear these things is simple...because they wouldn't look better, or even remotely as good.......as they do with the bases already featured with these characters. And I think you'ld also be hard pressed to find a single LOTR PF or maquette collector who thinks these two lines would be best served or even remotely as good as they are if SS chose to go with simple black bases instead of the ones they've chosen.
Do I think the bases SS are incorporating within the maquette and PF's lines are light years ahead of the majority of SSW bases?....absolutely. Not only do they allow SS to be more creative in terms of character composition [ie poses], they complimernt or enhance the characters in a way generic, black bases can never do.
Besides, the original base is just a generic piece of Middle-earth scenery. I might feel different if it were a piece of Weathertop.
If I had a dollar for every customer who wanted their framing to match the furniture in a particular room, or who wanted every picture framed exactly the same way regardless of the subject matter, mood, or colours of each individual print 
...I think I could probably buy a couple of maquettes with some change left over. But you're right, so many people really don't have a solid understanding of how framing impacts artwork, or in this case, how a base impacts a statue. 
