How to make sure that the latest (or at least later than what I have today) .net 4.0 version is installed?

Question

A very much related question has been posted here:

http://stackoverflow.com/questions/199080/how-to-detect-what-net-framework-versions-and-service-packs-are-installed

However, I found that .Net 4.0 conventions are messy. I need to hard-code some logic into an installer / installed product that goes like this:

if not RecentDotNet40IsInstalled():
    Panic()

If I get it wrong, then lots of clients will be unhappy.

I want to make sure that I am using the correct registry key, that I can rely on this stupid unorthodox registry structure.

Thank you.