The idea is that ‘some’ power will be saved if thousands/millions of people use Blackle instead of Google over millions of times.
But yes, the CRT/LCD thing is true, so that makes their concept incorrect.
I found out about this last year, liked the idea enough, even just to be ‘different’. I planned on using it as my default search, but alas, there is no Image Search, which alone, makes me boycott it.