If you read our very first impressions of the TSX (back when it was launched in 2003), you might remember that we came away really impressed with Acura's junior sedan. While we were smitten with the superb balance of the chassis and general competence of the car, we couldn't help but muse about how much more we'd like the TSX with 30-40 more hp and an even sportier demeanor. In fact, while we were at the press preview for the TSX, we asked some of Acura's product planning staffers if and/or when there might be a Type S variant of the TSX, and the general response was that Acura might play that card if they needed to when it came time for an MMC (see the genesis of the 2nd generation TL for an example).
At that point we weren't really expecting to see a MMC (midcycle model change) for the TSX until the '07 model year, but since the TSX is based upon the Euro- and Japan-market narrow body Accord (which launched as '03 models), the TSX benefitted from a refresh this year, placing its lifecycle in lock step with its overseas cousins. This carries the implication that the current TSX (CL7 chassis) will have a relatively short run of only 4 years, with a replacement (rumored to be based upon the Sports4 concept) due to appear in the 2008 model year.
On top of the relatively short run, the TSX has been a sales success for Acura from day one and continues to be an unexpectedly strong seller for Acura. Given these factors, it seems logical and likely that Acura decided that the "Type S" card didn't need to be played for this generation of the TSX. Instead, for the MMC we got a number of subtle (yet effective) improvements which add to the appeal of the TSX.