They do offer a new version of their app that works with the new operating system, and they do offer upgrade pricing. And old versions continue to work with operating systems that existed when those versions were developed.
Sorry, but complaining bitterly online about this just reeks of entitlement. It costs time and therefore money to support a new OS version. (Besides which, the new Bria apparently has other improvements.)
I looked, just because this person seemed so outraged, and the cost of the upgrade is $35 [1]. It appears Bria 4 launched 3.5 years ago [2]; if Bria 5 lasts as long you're talking about less than $1 a month. That seems eminently reasonable!
(Maybe this is a generational thing? When I started using computers, it was not unusual to spend $100 on a software upgrade.)
[1] https://secure.counterpath.com/Store/CounterPath/ProductInfo...
[2] http://www.counterpath.com/counterpath-launches-bria-4-softp...