Since this is pretty much the antithesis of vide(a)o game news and I'll be able to dig it up every 60 odd days...
The 'whole point' of steam is to allow you to have everything under one canopy? Not to, for example, make GabeN money? If you want the potted version of the reason I dislike steam it's that it wants to act as a gatekeeper over an open system, has monopolist power and provides no actual benefit over what being on a PC already provides. If steam did not have steamworks and did not latch itself lamprey like onto 3rd party games I would not care about it in the slightest.
And I already have my PC games under one canopy, it's called 'my computer' (or Cyrus to be technical, precursor to Xerxes)
If it's the same situation as here (and it is) it's ISPs mirroring steam's servers to save on international bandwidth, rather than anything to do with steam itself. I can, on occasion, get unmetered downloads from GOG because they've been cached as well, and that ain't due to GOG, it's my ISP saving $$$.