Term of service is the jurisdiction that everyone should be following inside the casino or in any gambling website, though most of the time it is being used and sometimes being abused. Since it is indicated on the terms that they can make changes on it at any time without prior notification to the players IMO they are on the right side.

However, as a gambling site or a business who needs customers to be profitable they might just somehow do efforts in notifying their players of any changes, in that case, they could avoid scenarios like this which could even lessen them not only a single player but could possibly multiply it if most would stand on the side of the complainant.

This is correct.  
Actually, I'm surprised that this topic continues so actively???
 It seems that we have already discussed that devs acted incorrectly with their "free money".  And the user was naturally offended.  Of course, to end the topic, devs would have to admit that they were wrong and apologize to the players.  And do not repeat this mistake further.  
That's all that should have been done, and not continue the correspondence in this topic.