if they need it they want it, if they want it they need it
Disagree. I want a new 2G iPad, but my 1G iPad works well enough and I don't need it. I would like one but I'm not going to express that desire with cash.
I see where you're going but I think it's an important distinction to make, especially with consumers. It's easy to take a sharp rational mindset and project it onto the fish in the stream... but that may not be the best model for predicting how they think about your products.
But consider something like legal/regulatory requirements. Perhaps you don't know about some law at the moment, but you should be complying with it. I have a product that fixes this problem for you. Until I call you, you don't want it but you still need it. When I tell you this, hopefully you'll understand and I have a good chance of a sale.
This is because, if your competitors have it, you must have it also. And if it exists, and your competitors can afford it, they will buy it.
It's a great feeling, I just hope I'm right!
And as barefoot says above, you can want a product without needing it.
Need/Want may be correlated, but they certainly don't imply each other, in either direction.
There is no insight to be gained from the distinction, it's semantic masturbation nothing else.