I think shows like The Biggest Loser are at least in part to blame for this sort of thinking. People watch TV and get the idea that losing 10 pounds a week is normal and losing just a pound or two is a big failure, when in reality a pound a week is pretty normal and two is freakin' fantastic. I think people forget that a pound a week (or even half a pound, or a tenth of a pound) will still eventually get them to their goal.
My mom falls prey to this a lot. She will go all gung-ho on her weightloss plan, and then calls me up saying, "I don't know what to do! It's not working! I only lost three pounds this week!" I've tried telling her that this is actually an awesome loss and she should be proud, but she gets discouraged and quits when she doesn't see the huge infomercial-style losses.
Former maintainer, now losing again in 2014 after my second baby.