I agree that Canon`s percentage from every bit of photo gear it makes is high. But you have to consider that these are not cellphones or some kind of consumer device that will sell in millions of copies. But even cellphones are selling for quite a big price compared to what it costs the manufacturer to produce. How much is an iphone going to sell contract free? $600? How much it costs to make? Probably $120-150. Or so people say. Nevertheless, you can purchase it with a contract so you`re getting in cheaper, but you`re still paying for it.
Now, how many tc`s Canon is gonna sell? I really don`t know the numbers, and i don`t really care, but it`s not millions. Not by a long shot. It`s probably in the tens of thousands, at best. They need to make a big profit from tc`s, lenses, accessories and everything, because those money is going into r&d, and paying all those engineers to satisfy your cravings for new and better lenses, cameras, etc. They cannot afford to stay behind everybody and sell these cheap, and you need to realize this. And i`m not talking about Canon only, i`m talking about every major photo gear brand out there. You can point to Sigma, but is Sigma a major player? I think not. Granted, they`re big enough and they`re doing ok, but they`re not among the best and that is because they are not making the profits Canon or Nikon does. And they also cannot charge more because everyone will then go buy brand item, not third party. They`re being the underdog, offering cheap items which don`t work as good as brand ones.
You cannot beat big companies as their game, you need to come with something else, in this case Sigma and all the other third party manufacturers are doing just that. I remember their quality control being less than satisfactory, and why is that? You guessed it, not big enough of a budget to work with, costs need to be cut somewhere.
And another point you may want to consider: How often would you buy a tc? Seriously! You bought that 1.4x, and that`s that. You may get the 2x sometime down the road, and you`ll stick with those for many many years. If you think about it, that`s a bargain.