We are the vendor for our product. Our requirement was that the product still had to run on SQL 2000 and also on SQL 2005. We discovered through testing that the behavior of certain queries was not exactly the same on level 90 as level 80 which forced us to run on SQL 2005 on level 80 for one version.

As a vendor you always have new customers and early adopters that want to run on SQL 2005 and a few customers you have to drag kicking and screaming to the new platform. They are the lowest common denominator . So you have to create an upgrade path that allows the late adopters to get there.