"- Ending support for 32-bit CPUs... Totally fine. To my knowledge it was only the very first Intel Macs used 32-bit CPUs, everything after that used 64-bit CPUs"
Its not only the 32bit cpu models, as per Apple's site, these are the only macs that can upgrade to Mavericks:
iMac (Mid-2007 or later)
MacBook (13-inch Aluminum, Late 2008), (13-inch, Early 2009 or later)
MacBook Pro (13-inch, Mid-2009 or later),
MacBook Pro (15-inch or 17-inch, Mid/Late 2007 or later)
MacBook Air (Late 2008 or later)
Mac Mini (Early 2009 or later)
Mac Pro (Early 2008 or later)
Xserve (Early 2009)
For example, there is a generation of Mac Pros (2006-2007 models with Xeon 64 bit cpus) that cannot upgrade apparently.