Well yes, exactly. I see people do that with all kinds of things. That is one of my biggest "mottos"....."don't give a command if you can't enforce it." Don't even say the word, "come" unless you're positive your dog is coming first. Get the pup to come by other means, running the other way, making silly, fun noises, hide behind a tree...something and then when it's obviously coming and very, very close to you, then say, "come." Then reward immediately. Or use a long line.
Same with any command. Get the behavior first, then add a command word while he's doing it and reward. Once he becomes quite good at it, then use the command word to get the behavior, but you better be able to see that it is carried out if you do use the word.
I know someone who says to her dog, "sit, sit, sit, sit." The dog is oblivious to her owner....absolutely out of control, not paying one bit of attention. And the owner continues to say, "sit, sit, sit, sit." It's unbelievable.
As far as understanding words, well....they don't at first, but are quite capable of learning many, many words in their lifetime.
Tone of voice means a lot to a dog. But we teach them what our voice means. Dogs primary means of communication is not verbal, but more physical; positioning, looks etc.... And they tend to become habituated to a certain voice. If you are loud, they'll get use to loud and won't respond to anything less....that is, if you haven't enforced or motivated and rewarded in a consistant manner. If you start out with a quiet voice, motivate and reward enough to get consistant compliance, then a quiet voice is all you'll ever need.
I see that too...people saying "come" in a loud, almost nasty, angry sounding voice. No wonder their dogs don't want to come. LOL.