It's called buying the version you need from the start...
You've obviously never written a program in a real work environment. People NEVER know what they need.
I doubt server requirements change so regularly it would warrant needing new server software every few months.
I mean people in general. People tend to buy what they think they need, not what they actually need. In this case, they're going to get screwed backwards and forwards.
A humorous example: an unnamed international company invested over $1,000,000 in installing IDS and IPS sensors to protect their network of Solaris machines. It turns out, the IDS and IPS sensors only protect against Intel-based attacks.
Of course, that has very little to do with the subject. I just find it a funny story.