Okay – it's answer your own question day. I knew I'd find it as soon as I posted.
http://www.adobe.com/content/dam/Adobe/en/devnet/acrobat/pdfs/iac_deve loper_guide.pdf
Page 13: For comparison, consider the following examples, in which you can see strings with "AcroExch.App" and strings with "Acrobat.CAcroApp". The first is the form for the external string used by OLE clients to create an object of that type. The second is the form that is included in developer type libraries.
-TT
