I would think there is a JW-appropriate explanation that goes something like this:
The GB must dress appropriately to be able to present to the "worldly ones" (*snickers*) they must deal with, as representatives of Jehovah's True Organization TM. They must defend Jah's name in court, and deal with Satan's attempts to discredit Jehovah. In order to protect "the flock" from "this wicked system of things", they need to blend in with the "world" in their necessary business dealings.
There, it's all explained! BB said it more succinctly. *shrugs*
Edit: An afterthought. What I like to call "The Ruling Elders" in my region, who lived in my circuit, were almost 100% upper middle class. They dressed in tailor made suits, and yes, pinkie rings were in style in the 70s. So why is it such a big surprise that these GB members (ie, the JWS' board of directors) are dressed in expensive (albeit often tacky) attire, and it's found acceptable by the R&F? hmmm....
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And, mark this, but I totally agree with the Red Dot. Yikes, is it THE END?! *just kidding, Minimus, but yeah, agreed*