I don't think that this is accurate. Companies are lead by Managers and in very few companies a manager has a sufficient technological background to make the right choice (talking about traditional companies, not high tech enterprises ;)
so all depends on the company and how well informed they are on the benefits to rewrite an application from php4 to php5.
True but suppose they have a working app, how likely is it they're gonna rewrite it ? :)
I heard a similar argument when PHP started to take off, something like a company using a perl script will not likely bother to rewrite it in PHP ... :)
I'm not going to say anything about Perl for one thing :)
It depends ont ratio cost/benefits, if you can prove them it can buy them a lot then all is good.
Arnaud.