I wrote the article, and I can give you three reasons the X1900 was picked over the 7900 GS:
1. Not all benchmarks tell the same story. At Firingsquad, the X1900 GT consistantly beat even the overclocked 7900 GS, sometimes by a notable margin:
http://www.firingsquad.com/hardware/nvidia_geforce_7900_gs/page5.asp
Even in some of the benches you linked to, if you read the whole article - the X1900 GT is neck and neck in moist stuff, but for a few games where there is a significant difference, the X1900 GT is way ahead - check out the Quake 4 benches.
2. Overclocked cards are vendor-specific and do not even have standard clocks between them. I'd have to recommend specific vendors which is beyond the scope of the article
3. The overclocked 79900 GS' tend to be inn the $220 range.
Sure it's only $20 more than the bargain X1900 GTs, but it's also only $20 less than the X1900 XT... who in good conscience would recommend spending $220 for a 7900 GS when they could get an X1900 XT for $20 more?
I even find it hard to recommend the X1900 GT at $200 because of the $240 X1900 XT, and I wrote that in the article.
So there are my motivations. Maybe you don't agree, but at least I hope you can underatand where I'm coming from. But right now, from where I'm standing, it doesn't fit. If the 7900 GS goes down to $180, or the X1900 GT goes up a bit, things will change.
They change all the time now. Come back next month and things might be totally different.