Wouldn't everyone agree that Dodge and Subaru had 2 different things in mind and 2 different markets in mind when they developed the SRT4 and WRX?
I wouldn't say that it's apples and oranges. I'd guess that they buyers of the SRT4 are primarily looking for the power, hence primarily drag racing (although I know that that's a broad generality). Whereas, I'd guess that the WRX attracts a very similar buyer, but it also attracts (and markets towards) those who are interested in road racing and autox.
When the Subaru came out, I think that it caught the attention and awed many across the US. When the SRT4 came out, though, I really doubt that Dodge was aiming specifically for the WRX. I think that they were trying to cow-tow to the Fast and Furious market.
I don't think I'd buy it, personally, when there are some other, superior cars available for not much more, but I admire what Dodge was trying to do (and actually achieved in my book). It is a powerful car. It's one of very few small displacement, turbo'd cars marketed today, and I'd argue that it has backed up what it promised. I think that with the LSD and some racing slicks, it could even be a pretty potent threat on the track (at least among the regulars who I see at trackday)
Speaking from my narrow experience, there is a guy who was autox'ing the ?1st gen SRT4 (w/o LSD) who placed 4th in either SP or SM.
...but to answer your question, I'd say that it's probably because of the additional displacement and probably the ECU is tuned more aggressively from the factory than the WRX is.