From the linked C&D article:

but there are a couple of good explanations. First, the WRX STI weighs a hearty 180 pounds more than the base WRX, according to our scales. Second, the STI and its closer-ratio six-speed manual call for two shifts to 60, while the regular WRX's five speed hits 60 mph in second gear. By the time the pair travel a quarter-mile, the '09 WRX loses some ground, though; both cross the line at 102 mph, with the base Rex edging out the STI by just 0.1 second, 13.5 to 13.6.

So...in a drag race the WRX edges the STI.

Point-to-point around a twisty back road or around a track I'm sure the STI does a fairly better job.

Sure you get more bang for the buck with the regular WRX. But I don't think most STI customers are buying it just to win drag races.