Interestingly, they are ignoring the 800 lb gorilla in the room: Often, even when people can speak instructions, they prefer to type them.
The only time voice commands are awesome is when you are alone.
I think you are right. It is one of the most fundamental problems with voice commands — the inherent lack of privacy. Interestingly, I saw an analysis a few years back that was addressing a basic conundrum. For decades, people had been predicting that we would interact with computers someday through voice, yet business analysts were finding that even when available, people did very little with voice commands, even as the technology was passing the 95% mark.
What they found was that there were several overlapping problems, that ultimately caused employees to go back to the mouse after playing around with voice input. First, the lack of privacy. Second, people don’t think very well while speaking. Third, a menu, or an icon, gives you a clear set of options, but voice commands don’t let you know what you can and cannot do. Fourth, the lack of precision (where the computer would think you wanted one thing, when you actually wanted something slightly different), drove people crazy, at least when trying to do meaningful work.
This analysis may be somewhat dated, but it wouldn’t surprise me if the basic findings hold true today. Voice may be great for entering search terms, or dictating text, or issuing the most simple of commands (at least, in private). But beyond that it doesn’t have as much potential as people thought back in the 70s.