There are 2 big differences with in game gold and crowns. Gold is infinite and only of value in game; crowns are limited and cost money in real life. Sadly the staff at Kingsisle are not all multi-millionaires who make Wiz for fun, so they need to be paid real money to pay their real bills. However, there are a few ways to earn 'free' crowns.
1. Trivia on the Kingsisle website. You can earn 100 crowns a day from this and also learn a few new things about the game as you do it. You have to get quite a high percentage of answers correct to earn the crowns so you might do best to look up the answers to get you started. It won't take you long to be whizzing through them and they soon add up if you do it regularly. You can do this while using your wizard :)
2. Earn crowns videos. You can earn crowns by watching the adverts on the in game 'earn crowns' feature. You might need to activate it in your settings and you will need to download Flash Player if you haven't already. You can earn 10 crowns per advert, which again, adds up quite quickly. The down side is that how many adverts available depends on your area so you may not get many. You also can't use your wizard while watching the adverts, but it is another way to boost your crowns :)
3. Daily assignments. You can get a few crowns from doing daily assignments. It's not very many and you won't get crowns every day but if you find them fun it's another little boost. You will also get some cool items from the chests, arena tickets and gold. On its own this will take a long time to accumulate crowns, but as an extra it provides a bonus :)
KI can give us these options because 1+2 both involve advertising and the Daily Assignments crowns act as an incentive to play regularly, which results in memberships being bought.
Perhaps you can think up some new ways for KI to make real money and pass some of it on to players in the form of crowns?