I heard Soundbooth is based on a Windows-Program Adobe aquired, a peace of software with heavily optimized x86-code. If this is true, it would need huge efforts to create a universal binary, not just a click in Xcodes compiler options.
Before people freak out, audio is a very different beast from every type of application out there. Audio apps need to do a tremendous amount of realtime processing, effects, synths, multi-track playback and at the same time record multiple live tracks and record live controller data. And all that stuff has to stay in sync. Many audio apps use parts that are programmed in assembly or at least programmed in C using hooks into CPU specific calls like Alti-Vec or SSE3. Apple tried to help out with the Accelerate framework to give developers one grammar that can translater into Altivec for PPC and SSE3 for Intel. I'm not an expert but I bet the framework is fine for playing back a stereo track or 6 track movie with Video, but how well well does it hold up with 24 tracks loaded with real-time effects? Probably not that well. Just like Apples VST to AU conversion SDK which helped out with some simple plugins but couldn't come near the depth needed for automatically converting some of the more complex synthesizers.
The point I'm getting at is that Soundbooth was developed by the former Syntrillium CoolEditPro team that Adobe acquired and changed it's name to Audition. These peope were an X86 team only, writing X86 exclusive code. Should they devlve into the "Accelerate Framework" only to possible run into a brick wall 6 months into development and be forced to rewrite code SSE native? If they use they Accelerate Framework they need to code bases, one for Windows and one for Macs. By saying "Intel Only" they probably just recycled the same X86 C or C++ code that they used in Windows and potentially someone or some group from the Macromedia team that used to make SoundEdit 16 or Deck created a Carbon timeline gui for the new C processing code.
So before you diss Adobe, thank them for giving the SoundEdit "guys" new purpose in their lives, because the alternative was no Mac version at all. Like I said Audio is a very different beast and I suspect this will be the first of many Intel only Mac audio apps. Indeed now is a great time to be a Mac gui coder.
Michael