I am curious to know how is Pixologic able to provide a free upgrade to all registered users when most or maybe all other vendors put a price tag on upgrades?
Thank you so much for making Zbrush an amazing work of art.
I’m just a user, but this is my 2 cents.
Most software companies don’t charge for point release upgrades, so I’m not surprised that 3.5 is a free upgrade. I’m assuming that they’re making 4.0 a free upgrade to grandfather people who have recently purchased 3.x.
Pixologic is still a relatively small company with only one product. They aren’t the only developer making sculpting software anymore so they have to find ways of keeping their user base from getting distracted by competing applications. That means releasing awesome free plug-ins at regular intervals, but it’s also maintaining good customer relations; and everybody loves free stuff. If they don’t charge now, that’s that many more people that may not switch to Mudbox or something else. And with all the cool stuff coming our way from Pixologic, who would want to? 
Thank you for explaining. I now realize why Pixologic provides free stuff once you become a registered user.