I've gotten some criticism for using the Matroska container for hardsubs. (No, we are not going to softsubs, and certain things have happened that have really hardened our stance against softsubs.)
One of the criticisms I've gotten is that I'm not using all the features of the Matroska container. The way I would like to address that is by an analogy.
Like many people in the United States, I drive a car. It's not the cheapest car, but it's certainly not the most expensive car. My car has certain features, such as a radio, power locks/windows, air conditioning, a fuel gauge, etc. Every car has a certain feature set. Some features are required by law, others are optional. Just because I have a feature in the car doesn't necessarily mean I have to use it. For example, my car's radio has access to XM satellite radio. Do I have to listen to XM satellite radio?
Now, there are certain features which are pretty much required. For example, brakes and tires/wheels are required. Of course this list is not all-inclusive, but hopefully everyone gets the idea.
To compare this to a video container, our required features are the ability to hold video and audio. Those of you familiar with Matroska know that it's capable of holding and managing a great variety of things, including styled softsubs and ordered chapters. However, just because a feature is there doesn't mean you have to use it.
I personally believe in keeping things simple. As long as things are kept simple, there is less of a likelihood something will break. In the case of our encoded video, the less someone has to do to set things up so they can play the video, the better. This does come at a cost to quality (as hardsubs require more storage space for the same quality), but encoding video is a matter of compromise between quality and accessibility. (Accessibility includes file sizes as well.) This is probably one of the biggest reasons why I like VP8 and WebM. The WebM video format is locked down in a way that ensures accessibility.