People tend to forget that Gargantuan is simply a 4x4 square suggestion. I can't remember what page it was on, but I believe the gargantuan entry said 4x4+. Elder Red Dragon or Orcus or whatever 4x4 is ok. But dude with planetoids orbiting him, I'll use 4x4+ thank you very much.
I personally have been pondering how to handle fights on this scale for some time. Still not sure, but those spheres in this article are awesome.
Oh, sure, it isn't an issue of the size category itself. I was more commenting on the basic situation itself, of fighting something so immense, and how to actually portray that in game. Whether the stat block is labeled 'Gargantuan' or not, it could use a small sidebar or similar giving suggestions on how to run such a thing.