Maybe I'm just being dense here, but
Now if a cell phone manufacturer also included a functionality of measuring water pressure then even this fellow will not need a wrist watch.
doesn't make any functional sense unless the cell phone is waterproof and can be strapped to a diver's wrist, which even at the miniscule size they make them now would be impractical for diving. And how on earth would the diver be able to utilise the tiny tiny keys with diving gloves on
I need a wristwatch which is analogue and has a large face, so I can instantly see the time at a glance. Mine does nothing else. And my mobile cannot fulfil that almost instant function for me. I'm not sure what else I'd need it to do, no date, no time, no alarm, and I'm happy with that.
Shouldn't I be?
Definitely Fia! For you as an individual your requirement is just to tell time without alarm, with analog, and so on. So you will choose to look at a wrist watch as a better option than cell phone. From a business' perspective, the organization that is manufacturing wrist watches sometime in the future will be faced with this question: do we have enough customers like Fia who want wrist watches only to tell time? If the predicted number is below a certain acceptable level, they'll obviously diversify/add new functionality to attract new customers/or close shop.
As far as water proof cellphone is concerned, I agree it is yet to be manufactured. The moment an entrepreneur or a current cell phone manufacturer figures that such a need exists in the market and there is enough potential to make money out of it, they WILL research it and develop it. This is Technical System Evolution. This happens, whether you or I like it or not. What the TRIZ body of knowledge is doing is putting all these so far ad hoc-ly done inventions into a concept called "Trends of Evolution" and now it has taken a further step to evolve the concept to "Directed Evolution" where businesses "predict" how the system will evolve in the future and whether it has reached its full potential...based on that they decide whether to continue to improve an existing system (99% of time this is what is usually done because many systems still wouldn't have reached ideality) or work on building a new system.
So your problem of "water pressure measuring" with wrist phone, and the size of buttons, display size, etc will more or less get developed as the need (from a business perspective) becomes apparent and follow the same trend of evolution.
Just look at a normal cell phone for example - the first ones were as big as cordless phones...they have evolved. There was only talking capability, now u can text, u can email, multi-media communication, etc. I won't be surprised if desktops become redundant in 10-15 years time. If the cell phones can start building on their camera feature to have a resolution as good as a digital camera and other functionality...why would the average Joe (not the photography experts and professionals) want to buy a digital camera when the same functionality, same quality is coming without having to waste space in your pockets? I still own a Canon EOS 300 film camera...the problem is I can't share my photos so easily with everyone. Had it been a digital SLR, it would've been much easier. In fact the other day I was looking on the web for a "film" SLR...you don't even find them so easily. The state of wrist watches will soon reach there. It just takes one second for an individual to get hit by the idea that "hey I can tell the time without the wrist watch" and you'll see the person will think 10 times before buying a new one (he may still use his old one until it gets spoiled).
As an individual we can typically respond in the following ways to change in environment:
a) Accept it and work with it
b) Ignore it and later find out you are left behind, and then accept it
c) Deny it and stay where he or she is in his evolution (professionally, personally, whatever)
There is a 4th response that concepts like NLP, Leadership, Vedas, TRIZ, etc teach: you be the one to make the change for others to follow...then you will not have to feel the discomfort of going thru the process of accepting it at all!
Edit: probably our in-house Economist Nick can add his perspective to the business aspect