And since they strip out the link, it's very hard to find attribution.
Most sites are essentially "stealing" content from their users -- the people who submit it and retain the copyright on it (or should, if they don't) -- so this forces me to ask the overriding question here: Who really cares?
I disagree that repurposing tweets is wrong. Many twitter-based barnacle applications do just that and no one raises a stink.
And Mahalo Answers doesn't remove attribution. They link to the twitter account that posted the question (http://twitter.com/fluther) on the page. This might not be the attribution you desire (and you might be able to pursue legal action), but the attribution is there, nonetheless.
If they maintained the integrity of the tweets -- complete with the links present in them, that's something else.