Well the catch would be this:
You are right, the developers need the money. That's why they introduced a few popular functions: First it started with the cups. In the cups you play versus teams from other countries, and if you are succesful (get into the first 8 in the end), there are some prizes. Ofcourse, these cups aren't free to play, each costs an euro (now you can calculate, some 5000 people join a cup, that's 5000 euros).
The next function that was introduced were the friendly leagues, costing 1 euro (or equivalent) each. In friendly leagues you can play against your friends, or just get in to compete against managers from the whole world. Each costs 1 euro, and seeing as it's pretty popular, MZ earns alot of money through this.
Next, MZ crew invented the "challenge top clubs" where you can challenge the 8 top division clubs from each country and play against their A-team, 1 euro each match, then "World Allstars" challenge, 1 euro per match to play vs the World Allstars, and finally, the "Greatest players challenge", 1€ to play vs one out of three best teams, managed by some well known managers.
As I saw, there are some 500 matches played a day, so that's 500€ a day.
Next, and probably the function that brings the most money: Analyzer and ManagerZone Live. To sign up for them, you need to buy a package, starting costs 2.95€ (better packages include some free cups, FL's, challenges etc.). The Analyzer and Live tools are made so that you can see your team actually play and correct their mistakes.
This is rather popular too, bringing quite some money in.
Finally, as some countries gained mobile paying access, ManagerZone added a 1€ registration fee, taken directly from your mobile account (this is to prevent cheaters).
As you can see, ManagerZone clearly gets enough money to pay their server costs etc.
Oh, don't forget MZ Hockey is coming out in 2 days, meaning the income will probably double.
Another thing, MZ is free to register and play, period.
All the other things...duh, who needs them...if you've got money to pay for 'em, then do it, but you can clearly play and have a great team without paying for more functions (silly old me being the Swiss champion, Ash playing in English Premier League, and more).
I hope I helped you realise what a great game this is...welcome to the world of MZ