This is the version number for the forms handling part of Acrobat JavaScript. It does not necessarily track the Acrobat version number, which is why there is a separate variable for it. There were very few JavaScript updates to Acrobat 8. I don't think anything was added to the forms JS so it makes sense that it would retain the older version number.
Thom Parker
The source for PDF Scripting Info
www.pdfscripting.com
Very Important - How to Debug Your Script