Versioning policies tend to be arbitary and often fail to give an accurate sense of what advances, if any, (and of any relevance to the user), have been incorporated.

It's also worth noting, in the face of the OP and clarification, that Perl versions => 5.almost-nothing are still in wide use and very effectively -- and for many intents, on something like par for 5.16. It depends on what you need... but in this case, the SOPW needs to recognize that the path forward is will the current version.

But back to the PHP comparison: while I don't use PHP4 or 5, with any regularity, I'd regard difference as more nearly akin to Perl 4.x vs Perl 4.x+1.