GW didn't do this for almost 25 years, and it was really bad for the game. Now they've copped on and are doing it - since 8th ed. was released, point costs have been changed twice already! And some of those changes hit the same units twice ...
(Cult genestealers going down to 10 points from 18, and then shooting up to 15 again.)
If you're interested, check DE Razorwings, genestealers, AM conscripts and some other things which were considered broken after release and got cuddled almost immediately. So, yeah, using GW as an example for NOT changing points is a bad idea these days ...