Since it's a meta search engine it could well be to do with their selection of searchees. I use ixquick and that hits about half a dozen SEs. They used to include yahoo and bing (roughly the same now), blekko and wikipedia. Unfortunately they changed their site (why do SEs do that?!) and now they no longer say where they get the results from.
I used to use StartPage, which claimed to be the same as ixquick. I stopped using it when they began fronting for google. :(
Any more information about it? I'm checking my traffic and.. my websites are increasing traffic from this 'peculiar' search engines.. and conversition too... detail I'm getting traffic from keyword that I don't have good optimization in google, yahoo & bing.