There's a real art to game monetisation. There's very evidently an amount that people are perfectly happy to pay for each type of microtransaction but then no more. We've seen angry player criticism of a number of monetisations: Oblivion's horse barding came out when people weren't ready for $2.99 for a piece of fluff armour. Runes of Magic's $10 basic mount was indignantly protested by a section of the player base although enough of them accepted it to pave the way for WoW's very successful $25 mount. Left for Dead 2 suffered a player boycott. Champions Online charging for respecs got people cross, not because the charge was out of line with other microtransaction charges (cf account transfers) but because the idea of paying for respecs was new and strange.
There are some general rules then it's this - it's safe to copy what people have got used to in other games and even add a little bit. At one point a monthly sub of $15 was new strange and unwelcome. I quite happily played Diablo 2 when Ultima Online started because I didn't see what the $15 was for and didn't particularly want to pay it. However once I'd paid $15/month once on a game I loved then I had no longer a barrier to paying it for future games.
Monetising for children is an especially fine art. The sneakiest method I've heard of was one Jesse Schell mentioned at DICE. What the developer is doing is giving children free access but allowing them to accrue store points that can only be spent if they subscribe. The free game is fun enough to keep them playing but there's a growing treasury of store points that they can buy loads of cool things with if they can just persuade Mum to pay a sub. They can play as long as they like completely free forever and of course the longer they play the more desperate they will be to get Mum or Dad to pay. Insidious, eh?
Not all monetisation has to come from players. Advertisers, lead generation companies and marketing people are very interested in accessing game player bases. This is a particularly sensitive form of monetisation as DDO's offerwall fiasco demonstrated.
It really is an area where the industry is taking rather clumsy baby steps and companies are occasionally provoking outrage as they fumble their way through this new science. It doesn't help that some of the steps are just plain stupid (US Allods players rather objected to paying ten times what Russian Allods players pay - who knew?). As a result developers are proceeding with a great deal of caution and know very well that this caution is causing them to leave money on the table.
However the fact that the industry has moved from a paradigm of everyone knowing how much games cost because they all cost about the same to a paradigm where each game that is produced requires its own monetisation means that we are heading into a period of massive change.
I'm sure that most new MMOs won't have a pricing structure quite like any other game before it, each will be unique as companies continue to experiment and push. That doesn't necessarily mean giving away less for free - the notional nirvana is a game that is hugely accessible but draws people in to spending Magic: The Gathering level sums to play at the top level. (I spent about £5000 on Magic during the 18 months I played it).
Non-video games of course have many examples of games that most people simply can't afford. Polo requires you to turn up with your gear, stick and horse as well as paying the club fees which for my local club are £70 per player per hour. Playing cards in the casino is sufficiently expensive that for most of us it's only something we'll watch James Bond do.
And of course the more the industry chases the accessible yet expensive nirvana the more pressure will build up in the player base for something cheap and fun that doesn't shake them down every chance it gets.
It's going to be an interesting decade in games marketing.