I'm not sure I follow your reasoning. If backward compatibility actually was that great and clients actually believed it, why would they wait around for ages b

I'm not sure I follow your reasoning. If backward compatibility actually was that great and clients actually believed it, why would they wait around for ages before upgrading? It should be a no-brainer. Instead, what I've seen in practice, is that people are very much afraid their random crap will break. They absolutely don't believe the backwards compatibility is a thing, at least not without "testing". The company I work for has a bunch of software that the providers only "support" on versions of windows server that are at least one or two steps behind current. Hell, I've even seen this for things which seemed pretty basic (think random web app) running inside a JVM. I don't personally use windows all that much, so don't really have first-hand experience, but my impression is that people are very much afraid of upgrades, even when running pretty "basic" things (as in "office software", not things which manipulate low-level, old interfaces or similar)