Adobe CS1 released Sept 2003. CS2 released in April 2005. CS3 in April 2007. CS4 in October 2008. CS5 in April/May 2010.
Mac Pro August 2006. (7 months before CS3)
Quite simple - Adobe has roughly an 18 to 24 month major release cycle. Apple switched processors in the middle of Adobe's cycle. Adobe added universal binaries in the next release after the Intel switch. What more could they reasonably do?
Yes, CS4 was 32-bit for Apples and 64-bit (in parts) for Windows. This was mainly Apple's fault, for changing their announced roadmap and dropping plans for 64-bit Carbon.
Fast forward one year, WWDC 2007, and it is announced that Carbon64 won't be provided.
Adobe was aware of these changes WAY before we were told. They knew already and decided not to switch to cocoa. They were aware of Apples plans as they been briefed.