Voice control is really bad for various things, so it won't ever completely take over. Among the things you wouldn't use it for are:

1. Are you going to browser your movies by voice and remember which of the hundred movies that it (took an hour) to tell you are available you want to watch?
2. It's good for announcements at the time but very bad for getting an overview of status after the fact. A touch screen can show you a lot of information very quickly.
3. Any guests that come over will have no clue what to do for a voice control interface because you have to know the commands before you can invoke them. A well designed touch screen can allow someone to quickly find what they need.
4. Administrative or sensitive tasks. Until we have high quality voice recognition (as opposed to speech recognition) it won't be possible to do any of these types of tasks via voice control unless you live completely alone. Touch screens easily allow for password protected and discrete control over such functions.
5. You can put a touch screen out of the reach of a small kid, but you can't prevent them from accessing voice commands.
6. Some things you neither want to know about when it happens, nor want to sit around and listen to a long list of things read out to you after the fact. For these, touch screens are obviously far better. You may not want to know every time a window is opened. But you may want to know which windows are open, which you can trivially and quickly determine on a touch screen but waiting for two minutes while a voice control system reads out the list would suck.
7. Would you rather take 5 seconds to see the next ten days of weather forecast data laid out visually, or listen for 2 minutes while the information is read out and you try to remember what the conditions were on the days you are interested in?

I'm sure that there are other examples, those are just off the top of my head. Of course some people have voice control fever and will claim that none of those things make any difference at all and why would anyone want to ever pick up a touch screen or walk to a touch screen. But I think that, clearly a pure voice control system will have limitations and annoyances.

And of course what a lot of the above implies is that automation systems aren't just about control, they are also about feedback and information, and that pure voice control solutions are really bad at certain types of feedback scenarios which visual systems handle perfectly.