I think that cuts both ways. If the computer can be trained to understand the user's intent, that seems like a better solution than forcing the user to think a different way.
Which would you rather do? Be forced to state your lighting preferences in candlepower, or have the computer learn that when you say "subdued lighting", you mean "12"?
Very true, but this is one simple example. Look at what Wolfram Alpha tries to do for even more complicated examples. If I put in "if I am traveling at 60 miles per hour how many hours does it take to go one hundred miles" it gives me an answer of 6000 seconds (1.66 hours). Very intuitive, and it actually ruined my example because I did not expect the site to understand what I was saying.
But if I type in "how fast do I need to go to travel 100 miles in 6000 seconds", now it has no idea what I'm talking about and instead gives me a comparison of time from 6000 seconds to the half life of uranium-241.
Now, when I get that result, I don't usually just give up on trying to figure out the answer. Instead I try to figure out what the computer expects me to say. Through some trial and error, I can shorten the query to "100 miles in 6000 seconds" and boom, I get the answer of 60 miles per hour. Instead of natural language, I'm using the search engine like a calculator.
The computer has just taught me how to use it. Ideal? No, but we work within the reality we're given. 12 candlepower is dim for you but for someone with decreased vision, that might be completely dark. The computer doesn't know unless it's taught, and we know from looking at history that users would rather the computer train the user than the user having to train the computer.
You asked: "how fast do I need to go to travel 100 miles in 6000 seconds"
Which is equivilent to saying "at what rate do I need to go to travel {rate}". It's a nonsense question, you already know the answer. You need to go 100 miles per 6000 seconds.
What you should have asked is: "100 miles per 6000 second to miles per hour", which it will happily convert the rate you gave, for the one you really wanted.
I guess what your saying is it should be able to figure that out, but at some point, the old phrase "garbage in garbage out" surfaces.. You never told it to convert the unit.
Wolfram is, and has always been, much more inclined to understand you if you work out what exactly you are trying to calculate before hand.
Some phrases exist as a "wow, 1 million people phrase this problem this way, let's throw that in." The fact it can take an easily dictated, albeit strictly phrased problem, and get you your answer is really what I love about it. Now if Siri would just stop sending stuff to Google. -_-
What if you could define the equivalent of Bash aliases via voice control? This would allow users to tailor their experience from the default (possibly complex/unintuitive) commands to their own personalized ones.
Example format: "Computer, define X as Y"
"Computer, define subdued lighting as set lighting to candle power twelve"
Then the VUI just adds a new entry to the voice commands where saying X results in Y.
Which would you rather do? Be forced to state your lighting preferences in candlepower, or have the computer learn that when you say "subdued lighting", you mean "12"?