Yes and no.

Power-law relations mean that a small number of domains will account for the lion's share of low-relevance results, and filtering those out will result in dramatic improvements in relevance.

That small set is probably fairly dynamic, however, and will likely change at a fairly high rate over time.

Penny-ante sites are less likely to appear in generic results, but might well be whatever the spam/phish term is for junk general Web search results.

We may well come to rely more on whitelisting, but I think at least for now that's not necessary, largely due to the dynamics of publishing / attention economies themselves.