As a teacher, it was a yearly rite to have some student miscreant whine in my ear "but I changed the words" when I pointed out that his research paper was rife with plagiarized material. So it shouldn't be surprising to hear a Presidential candidate caught with his hand in someone else's word hoard say "I really don't think this is too big of a deal."
Now plagiarism is sometimes inadvertant. We read or hear something nifty and over time forget the original source and congratulate ourselves on our marvelous turn of phrase. But anyone who sees the side by side video of Deval Patrick and Barack Obama on Babalu would be hard pressed to describe it as anything other than deliberate intellectual piracy. Why describe such a small thing in such dramatic terms? Because it is dishonest. It involves taking someone else's work and presenting it as your own. Because it insults the reader or the audience. The writer or speaker is getting one over on same. Because in a presidential candidate it implies a willingness to cut corners to achieve one's aim, in this case getting to the presidency. Finally it demonstrates an intellectual shoddiness that might not be the best characteristic in a president.
I once saw an acquaintance give his dog a swift kick when he thought no one was looking. It was not a big thing. The dog was not particularly hurt. It didn't even whimper, just made itself scarce. I wasn't about to call the humane society on his owner. But that small gesture spoke volumes about the owner's character. From that day forward, I developed a distaste for this particular acquaintance.
Obama is right about one thing: words do matter, especially when they're not your own.