I'm sorry Steve but I think you are confused (I didn't say Voltron came before Transformers, sorry if I implied it did). And, Macross did come first of these. Strongly inspired by Space Battleship Yamato. Macross inspired the American Robotech. Robotech inspired Transformers (a knock off of a Japanese version, and Transformers along with most of the '80s cartoons we all love were made possible by Ronald Reagan). Transformers caused Go-Bots to come into existence along with Voltron and most of the other major big robot or "combining" cartoons/fads/nostalgia pieces we know.
So I guess it actually all goes back to Space Battleship Yamato. Oh and here's some dates (can we guess what I spent my childhood doing?).
Space Battleship Yamato 1974
Macross 1982
Transformers September 1984 (although more exactly 1983 for the toys by Takara, which predate significantly the animated series and note the direct relationship between Jetfire and Macross)
Voltron October 1984
Gobots 1984 (1983 for the toys, after Hasbro introduced Takara's stuff as Transformers) and then 1986 for the film
Robotech 1985
I guess this is my roundabout way of saying that these all draw their influence from anime so yay anime!
Steve I know you enjoy anime and Voltron so you should check out Beast King GoLion and Kikou Kantai Dairugger XV. Those are both credited as being the direct cause of Voltron although it was inspired by the genre and form used by Macross (inspired by Space Battleship Yamato), which inspired Transformers. Talk about a convoluted history.
Regarding that site the owner has a FAQ at
http://www.merzo.net/faq.htm. That may be helpful to determine how he came about the sizes he did. I don't remember what the BFG fluff lists for actual sizes but 7.5km sounds about right to me but don't quote me on that.
Sorry for being terse in this thread. In the grand scheme of things none of this matters anyway.
So there's a Voltron film coming out? Who is starring in it? Might be interesting.