Missing the point...
Your analogies don't exactly mesh with what he was saying. Releasing a BT keyboard for the iPhone would be more like them releasing CRT cinema displays because people prefer the resolution/refresh rate or whatever. All the analogies you made refer to simply different sizes/qualities of the same technology. Touch tech is the way of the future, and I applaud apple for embracing it. I do, however, see the appeal in the ability to tether a keyboard through bluetooth.
[Oop. Just noticed what you said at the end about seeing the appeal, but this kind of applies to other postings as well as yours so I'm still posting it with this small edit. By the way. I don't think anyone is knocking touchscreen. A new technology need not completely usurp a traditional one though. There are people working on producing tactile feedback for touch technology (giving the feel of touching a button even though one isn't there - think it's something to do with vibration or electromagnetic fields but memory is fuzzy on the exact technique) so maybe touchtype keyboards won't dissapear as such but just go virtual - but obviously only on devices larger than the iphone.]
You are making the massive mistake of equating new with better.
Until a new technology can do BETTER than an old technology it will not usurp it.
So let's look at the pros and cons of different text entry types:
TOUCHSCREEN:
Pros:
Great on the go, and therefore good for text messages
Cons:
but occasionally you can mistype and the suggestions for spelling corrections are nowhere NEAR good enough yet. Obviously that can be improved with upgrades but I'd say the typing speed would be 25 words per minute max.
VOICE RECOGNITION:
Pros:
Types what you speak
Cons:
In a quiet office or washroom, maybe. On an iphone with traffic noises in the background and your friends "Hey what's that you're doing" "shut up I'm trying to use voice recognition" interrupting what you're doing? Not likely. Oh and forget it if you have a weird accent. I think apple said it all when they printed the t-shirts for their voice recognition group years back. They bore the slogan "I helped Apple to wreck a nice beach". Give it a couple more decades of intelligent word-recognition algorithms, voice type and accent algorithms and advanced noise filters and even then I bet it will still 'hiccup' every now and then..
BLUETOOTH KEYBOARD:
Pros:
If you know touch typing and want to write e-mails, documents and long notes then there's no other option. There is no way I could get up to 50 words per minute on an iphone touchscreen and my tt speed ALWAYS exceeds that even at my slowest - even with this faulty keyboard (sticky 'c' button and spacebar). For people who use the iphone as just a phone and something to write texts on and maybe pour their ibeer from iphone to iphone (sorry, just a totally pointless app I saw the other day - no way I'd pay for THAT even at 59 cents) then, no, you don't need a bluetooth keyboard. Until they invent something better that can be used quickly and accurately in a noisy environment.
Cons:
Potential for mechanical failure. Can be bulky. Not so fast if you don't touchtype. These are the only cons I can think of and the first two aren't often the case with quality keyboards. Something like the think outside stowaway universal bluetooth keyboard (catchy little title!) would pretty much eliminate the first two (folds away to roughly the same size as an iphone, maybe a little bigger, but folds out to full size keys making touchtyping possible. Exceedingly good build quality making key failure unlikely for a very long time) and a few lessons in touchtyping eliminates the third.
SLIDE OUT KEYBOARD
I'm not going to even bother with pros. This is too small to touchtype so why would you need it? The accuracy rating would be roughly equivalent to that of the iphone touchscreen keyboard. Would bulk up a slimline device. If I'm going to bulk up my iphone I'd go for larger battery capacity, built in proper GPS, a larger hard drive, video out socket and SD card reader before I went for a slide out keyboard. Heck, I'd NEVER go for that keyboard...