The point is that by insisting on people having to use MS Office documents it is giving a license to MS to print money because there is no competition. MS owns the file formats and change it all the time to frustrate anybody who tries to make a compatible product. It has long come to the point where even MS don't know what their file format is but instead relies on code as documentation.

As for computers, there is a hugely competitive market for it - you can buy branded, unbranded, build your own. So your analogy is incorrect.

Notice how every month the price of computers drop and their capability increases. Notice how say 10 years ago the cost of the OS is about 10% of the cost of the computer, but now the OS (Windows that is) probably costs more than the computer yet the computer is orders of magnitude faster/bigger/better.