Operating systems for gaming computers? I suppose your Playstation and your Wii and your Steam Machine run windows and WINE doesn't exist? Dude, don't confuse a monopoly with having a big market share.
De Beers managed to get to 85-90% of the world market for diamonds, not quite an actual monopoly... but as the diamondmarket is international, couldn't get all the governments to protect their market position by granting an actual monopoly and requiring their customers to purchase only their products. Guess what their market % is now? 40%? Lower? I guess they didn't have a natural monopoly after all.... market forces and all that.
Monsanto? No need to even go there in terms of IP. There are hundreds of seed companies farmers can buy from. Yeah, Monsanto is one of the biggest (at around 35% of the corn and soybean market share, just below DuPont) because many of their customers like their product combinations (pest control + seeds that resist it), but if another company came along tomorrow offering a better deal, how long would their market share last? One season, two? You're reading too much anti-GM propaganda and not looking at the actual facts.