pds41: [...]
Most legal definitions of monopoly power start at 25%
[...]
amok: That does not sound right to me, and i have never seen such a definition before. not sure I have even seen a "legal" defienition of a monopoly, i am not even aware that any such definition existed. (i know about "legal monopoly", but that is something different entierly). Surely it is dependent on the market and how many competiors there are in it? (e.g if it is three competitiors, then they can not have less than 33%, which means that each of them would be a monopoly if they have equal market share).
Do you have any sources I can have a look at? it would be interesting.
edit - in any case, anything that is legal is bound to the contry which those laws operate within. if you are in the UK, and use a UK legal framework, keep in mind that Steam is operating under USA law and legal frameworks. thogh if you have those sources, no matter from which country, I would be grateful.
There's a difference between the pure definition of monopoly (one company, 100% power) and the legal definition, used in assessing whether something could be to the detriment of consumers. While I can't quickly locate the 25% figure in the UK legislation (it's probably more a statutory instrument than being codified in law), I'd also point out that monopolies aren't automatically unlawful in the UK.
The 25% comes from the old Monopolies and Mergers Commission in the UK, who could review once market share hit 25%. Note that they were replaced by the Competition Commission and more recently the CMA. They have a guide on mergers that they can look at (
https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/970333/CMA18_2021version-.pdf) - given they are most interested in mergers giving monopolistic power, the 25% on page three is quite telling) Other than that, the main references are in school and degree level economic textbooks - which admittedly aren't as good as a direct government source. The 25% is likely to also exist in any countries where the legal system is derived from the UK legal system.
In your example, three companies with 33% share each, you've got a classic Oligopoly. However, each company could also be exercising monopoly power given their level of market share. In that situation, any mergers would come under extreme scruitiny due to the concentration of power. You might also have a cartel if they are colluding...
I agree with your point on Steam being subject to US laws - but if they tried to acquire Epic (as an example), it could be blocked by competition authorities outside of the US. This is one of the areas where local jurisdiction doesn't usually come to the aid of companies.