It's not standard and it's not pleasant to most ears, but I think over the last 20 (!) years of development the Trolltech guys have tried to make sure they could advance Qt and make a living doing it. I respect that a lot.
OSS was a completely different animal back when this thing started. And it was forward thinking to avoid the whole problem with people demanding free support and bugfixes for open-source code.
Not saying that this is wrong, just that it's no wonder if they think this to be FUD if one isn't familiar with the rule.
As for the reasoning, a customer developing their product for years in-house and switching to commercial just before releasing would definitely place Qt financing in a shaky ground when compared to traditional commercial frameworks.
