You mean, frowned upon by the company behind the game? The difference is in ownership. A project with decentralised ownership, owned by token holders, is more interested in a fair environment, keeping all rules transparent, and only that the project is potentially profitable for the best players instead of being a profitable business for a company.

A games company for an MMO without a blockchain wants monopoly of selling the in-game currencies, and don't want competition. Or, they want to balance it so that in-game currency purchases is not available at all - if it is a premium subscription business model.

Parsec Frontiers is a project which changes all this. Yes, it is ok to trade in the currency - because the project was funded by the original token holders who received the tokens, instead of a company investing in a project and requiring an ROI. So, that is the big difference.