Huh. The only thing I've gotten from this thread so far is that someone in the UK has no idea what a monopoly is. No, your definition of a monopoly is so far from "accurate" that it's ridiculous. A monopoly prevents competition. Valve hasn't. What exactly do you think that they have monopolized? Requiring you to run a software program means monopolization? No. That's called DRM. A company protecting their software from being pirated has next to nothing in common with a company crossing the boundaries on preventing competition.

Valve is not the only seller of ANY product other than their own games.

Your speculations are a complete joke. You are fear mongering over something that would be horrible horrible HORRIBLE bad business on part of Valve. They are doing great in revenue as a result of their distribution system and are making money hand over fist on sales that publishers and developers are incredibly happy to take advantage of. Never before has their been an easy to find marketplace for video games that include all the big names in PC, right alongside indie developers. And more often than not, indie developers will have a spotlight right on the homepage providing a sale for those games.

Did you sleep through economics? Using your econ book as a pillow apparently gave you your definition of "monopoly" as well as your thoughts about where Valve is going to go in the future.