Are you working with a 64-bit version of Windows? If so, the registry keys for 32-bit programs like Premiere Pro CS4 will be a little different:
Does that key exist in your registry?
it definitely does. So, a followup question concerning retrieving common plug-ins directory: now that there is a difference in where to look up the path, a good installer on windows should be ready to handle both cases: 1) installing on 32 bit only os, in which case the path would be where docs say it is, and 2) installing on 64 bit machines, in which case the path location is where you pointed out? Also, to double-check, plugin location on mac hasn't changed from /Library/Application Support/Adobe/Common/Plug-ins/[version]/MediaCore , right?
This Wow6432Node is for the specific case of installing a 32-bit app on a 64-bit OS. And it's not specific to Premiere Pro CS4, but has to do with the registry redirectory on 64-bit OSes: http://msdn.microsoft.com/en-us/library/aa384232%28v=VS.85%29.aspx
Since Premiere Pro CS5 is a 64-bit native app, it will once again create the registry keys on a 64-bit OS as originally documented, without the Wow6432Node.
Also, to double-check, plugin location on mac hasn't changed from /Library/Application Support/Adobe/Common/Plug-ins/[version]/MediaCore , right?
Yes, that hasn't changed.