portversion and distversion - why not?

[Andrew Pantyukhin]

Portlint says:
FATAL: Makefile: either PORTVERSION or DISTVERSION must be specified, not both.

Can somebody please explain why? It comes in handy
to be able to define illegal distversion instead of redefining
the whole distname. B.p.m was designed to handle two
different variables in the first place. Should we really
abstain from using this functionality?