I need information (preferably hard numbers and charts!) on the
"typical" commerical (shirkwrap retail) software sales lifecycle.  By
this I mean the following: assume that company X introduces product Y
(example $20 to $200 personal productivty software or utility) into
the market (retail, internet, or both).

a. How do these sales decline over time? What is the "shelf life"
before a new version must be introduced?

b. How do these sales typically change as new versions are introduced?
v1, v2, v3, v10, etc.

I am not interested in the software engineering development life
cycle, and neither for high-end $100K custom enterprise solutions. I
am interested in typical software that consumers and small businesses
would buy, like utilities, word processors, graphics programs, and the
like. Think Quicken, Adobe stuff, Symantec, Microsoft, etc.

I understand that every product is different, and marketed
differently, however any data on this that is available I would be
interested to see. You can assume that the product is not marketed
poorly.

Thanks.