Earlier quoted context omitted.
But also, from the immediately preceding paragraph: "Several later studies did appear to confirm its findings — for example, Bozarth, Murray and Wise in 1989, also published in Pharmacology, Biochemistry and Behavior — but nothing came of those either." That paints a confusing picture, so without looking at the specifics of the later studies for possible differences, I think it's hard to come to a conclusion.
Wikipedia isn't so good when it comes to drug related topics. Or rather, it is atrocious since the linked study ( http://wings.buffalo.edu/aru/HOUSING.html ) arrives at the completely opposite result Wikipedia claims. It's an interesting read because it also discusses why setting up a study to fairly measure voluntary drug intake among groups of mice is very hard.
Wikipedia allows public editing. Did you amend the incorrect claim?