ASIC's consume very little power compared to a PC. One watt per gigahash is a rough value, although most promise quite a bit less. You'd need about 100 PC's, at 300W each, to produce a gigahash, using the assumptions in this article.
[EDIT: Corrected the numbers to match what you wrote. It is irrelevant, though -- if you get a gigahash for X watts with PCs, you'll use X watts to get X gigahashes with a 1W/gigahash ASIC.]
To put it another way, not going to 30kW of ASICs is equivalent to taking 30kW of PC mining hardware and turning some of it off (in a pre-ASIC world where PCs are the most efficient mining hardware available).
I don't think we'll get to a point where BTC has a significant footprint anytime soon.