^ In fact, if you get few good win in Demo mode, it does not mean that the casino has intentionally made demo algorithm more generous. Such a conclusion should not be drawn from short sample. Because in random game both good run in demo and bad run in real-money session can be normal.
Another important thing is RTP. You know, same slot can have multiple RTP configuration and actual RTP can change depending on which version the casino is running. So it would not be right to call a rigged demo if real-money result is shown differently from demo.
I personally do not consider demo mode to be substitute for real-money gambling. But it is useful for understanding the mechanics, bonus feature, volatility or interface of any new game. However, the biggest mistake IMO is to deposit real money after seeing a few win in demo. Short-term result in RNG do not create any reliable edge.
Of course, no one calls the demo mode rigged. It's not real-money gambling, so you definitely can't make any accusations or judge the game solely based on how it behaves in demo mode.
I was only talking about my personal observations, I personally seem to have much, much better luck in demo mode. I've often won unrealistically large amounts there, while I've never had anything even remotely comparable happen when playing for real money, despite all the time I've spent playing.
So, personally I can only conclude that there is some difference between playing for real money and playing in demo mode. Or maybe it's my luck playing with me so skillfully.
Demo mode is much more friendly to players than the original money games. What we must understand is that the mode changes when money is involved, so we possibly win more when playing demo, but the same winning system does not apply to the real game.
One thing that distinguishes both modes is the algorithm which applies to all games, be it slots or blackjack. As long as you are playing the demo version, you can never have the same system as the real game.