Why would giving money to the rich motivate them, but giving it to the poor make them lazy?

Washington Post cartoonist Tom Toles seems to be poking fun at that idea in this Cartoon from the 12/4/2013 issue. Giving $100 to someone who already has more than they can reasonably spend doesn’t seem likely to alter their behavior in any important way. But give that same amount to someone out of a job and hurting, and it might be what it takes for them to afford to clean, and press their clothes and pay the bus fare to go get themselves a job. It might be what keeps a roof over their head, keeping them from becoming homeless, which would likely end up costing them their job.

Of course, a poor person might blow the money on alcohol or drugs, but then couldn’t a rich person decide a windfall $100 should be spent in the same way? Where does this idea about welfare only working when it’s exclusively directed to the very rich and to the type of people also known as corporations come from?

NOTE: Normally, I ask one question a day and try to comment on all the responses. But I have too many questions bubbling up that all are time-based and need to be asked now. So forgive me (or perhaps feel relieved) if I am unable to post an acknowledgement of each response.