In my humble opinion it's all about money.  If E-Frontier only limited the upgrade to Poser 6 owners, then they wouldn't make as much profit.  Everyone know's how that goes.  Money makes the world turn.  Bottom line is, it's a shame that companies don't really worry about what the consumer wants unless it makes them more money.  I for one pre-ordered it, but that's me I'm a Poser junky.