I'm not sure they speed is such a big deal, but I think most people don't speak clearly enough for Speech Recognition to understand. Even with my odd accent, it responds pretty well but then, I don't blend my words a lot, the way most people do.
I'm sure if the people on Star Trek spoke the way most people do, they wouldn't get good responses either.
This post delivers:
Picard: Computer, shields up!!
Computer: Knock, knock..
Picard: Whut?? No, I said shields up!!
Worf : Sir, there's Klingons off the starboard bow.
Picard: I know! Thats why I'm trying to get....
Computer: Self destruct sequence initiated.
Picard: What!!
Riker: Why the hell did you do that?
Picard: I didn't! Honest.
Geordie: Sir, I think we might be able to roll back to 10.5.5, and then reapply the patch. It looks to have broken our wireless network, and is interfering in the Voice Recognition Protocol.
Picard: Geez, it's like 10.5.2 all over again.
Worf: Sir, the klingons...
Riker: Stuff the klingons. I can't play WoW
Computer: 1 minute to self destruct.
Riker: Oh yeah, forgot about that.
Picard: Geordie, do something!
Geordie: Look, I cant hold the shift key any harder and it wont boot any quicker....
Worf: The Klingons sent us a message, Sir. Open Terminal and type, without the quotes, "default write /Library/Preferences/voice.plist -encode 0 -w -a"
Riker: Crazy jugheads...
Picard: Do it!
Computer: Sequence interrupted.
Picard: Whew, that was close...
Riker: Awesome, full signal strength. Just got to level 70. Got me some ganking to do.
Geordie: Computer, run system diagnos
Computer: Knock, knock....
Picard: Oh for the love of God....
</nerd>