Having the URL on the screen doesn't do any harm. Having the URL be missing from the printed page does more harm.
"Harm?" This feature was only introduced last week. Were we somehow hurt by the lack of this text before?
The phrase "From Wikipedia, the free encyclopedia" makes the attribution clear, IMO, and most browsers print the URL in the heading of each page by default. This, however, is hardly the point -- I'm not arguing for the removal of the text, as most have noticed, but rather for its re-implementation using CSS.