It seems as bitcoin value grows there are more and more people who try and take advantage of it.
well both of these have pros and cons of their own.
1) faucet is good because it gives you real money not fake or anything. and you can experience things in reality. and also it has the benefit of making some money from it. for example in a provably fair Dice site you can make a 9900x bet and get lucky and win a big amount (I think something around 0.02BTC). and also you can try out strategies with small amount. with faucet many will want to deposit more to try out a bigger bankroll.
2) demo mode is good because it can give you a big amount without the site worrying about abuse, and also it can be big enough to give the experience of a real game with real bigger amount. lets say 0.5BTC for example. and in this case you can experience the reality of having that much. although this may be bad for casinos because when people realize they can lose the fake demo amount of that big, they can easily lose their own money so they may be discouraged to deposit anything because of fear of losing money.