My reasoning is that a manufacturer like Nokia could neither be blind to the advantages of a perfect smartphone nor lack the expertise of proper implementation of the technologies into making such a device. They make a perfect smartphone and people buy it. Then what?
I suppose you think oil manufacturers know how to make cars run on water but are holding back that secret too?
This conspiracy theory stuff about manufacturers deliberately holding back a "perfect phone" is a total myth.
There's three main reasons for this:
1. People's tastes vary
You might have a smartphone with every available hardware feature at the current time, which is pretty much what the N95 was in early 2007, but 95% of people won't touch it because such a phone will be too expensive. The N95 launched for something like 600 to 700 euros, which is way way way beyond the budget of the average phone user, who prefers phones near the 100 euro mark. Price is a feature too, and the more hardware you add the worse the price becomes.
The only way to get mass sales for devices is to make them a reasonable price, which means leaving stuff out and making a variety of devices that serve the different priorities of different people.
I personally thought the 6120 was as close as I could get to my own perfect smartphone, because I'm not a huge fan of Wi-Fi and I don't really need a 5mp Carl Zeiss camera. It looked like a normal phone, it had the same size and feel of a normal phone, but it had just the right combination of features for my own needs. At the time I reviewed the 6120 last year I had an N95 on loan too and the 6120 felt like a much better phone, even though on paper it was technically worse. My idea of perfection is that fewer features are a great idea if it means a smaller, cheaper phone.
Others absolutely hated the 6120 because it had a small display, but that was part of the reason it was so small and cheap, which is what I wanted.
2. Technology doesn't stand still, so tech fans will never be satisfied for long by even the best model
AND... even if you did come up with some mythical "perfect" phone, how long exactly would it remain perfect? How long was 3G the fastest standard? How long will 3.5G be the fastest standard? How long will 16gb seem like a large amount of storage space for a phone? How long will people settle for non-touch phones? If phones all become touch-based, what happens if 3D gestures become more popular than 2D touch? No one knows the answers to these, yet manufacturers have to start planning for the future right now.
Phone technology moves on so so quickly that there's absolutely no point in manufacturers holding anything back because whatever they release will become rapidly outdated anyway.
I remember when the N91 came out I thought "They'll NEVER top that, it's got EVERYTHING", but just a few years later it seems like rather a primitive phone with its low res display and limited amount of memory.
3. Real people don't buy phones very often
For this conspiracy theory to work, it would have to force people into buying phones more often because they can't get all their features in one device. But this just doesn't match reality. Outside the tiny number of hardcore tech fans, real people only buy phones maybe once a year at most.
In those circumstances it wouldn't matter if someone bought a "perfect" phone because by the time they do their next upgrade the "perfect" phone will already be out of date as new technologies and components have become available.