OH KNOES I am not an enthusiast! LOL ok LOLOLOLOLOLOLOL I completely get the pc master race slants with comments like yours.
Serious reply: With a blower cooler it does not make a difference. With an aftermarket card, it makes a very dramatic difference - basically, the hot air is going to flow out of the rear exhausts of the card whether the card(s) are in a test bench or an enclosed case. Keep in mind, the hot air doesn't circulate around the cards with a closed blower, this is true whether an enclosure is used or not. Conversely, open air cards tend to do way way better on an open air test bench. I think that was his point. Although, he was facetious in the wording of it with the "any enthusiast would know this" comment.
Please note that i'm not saying that the blower cooler on the 290X is good at all.
I think it sucks and drags the otherwise great aspects of the 290X (performance) down. But the point stands that blower coolers don't matter on an open air test bench, while it does change results for aftermarket coolers to a degree. Then again, how do you test for this with an aftermarket cooler? There are thousands of cases so if a reviewer is testing an aftermarket card, he can't possibly replicate 100% of the conditions that a user may have. You might have an aftermarket open air card in a mITX case - so if a reviewer tests on an EATX monstrosity, his results will differ from yours. So I guess it's really a no win situation for reviewers even with an aftermarket card, you know? But the point remains that with a blower, it doesn't affect results, really.
edit: As others have mentioned, blowers do better in enclosures than they do on test bench environments because of fans and air flow as well.