There are no buttons for heating of seats on armature
 

Probably a lot. You will need to buy seats with the heated option as well as the switches to start.

Most manufacturers use one wire harness for a car model regardless of the options the car has. So while your car may have the wiring for heated seats, you probably do not have anything else that is required for them.

Not really.. all it means is that the wiring is there and nothing else. The seats do not contain the heating elements and of course there are no switches.

Are you sure you do not see the wiring for the airbags?

Hmmm good point...
As soon as I can, I will pictures of the bottom of the seat.

Use caution with that underseat plug, if ignition is turned on while unplugged,
it will cause an "Airbag Warning" that can only be reset by a dealer ($$$).

You can go to your dealer and get them installed. I don't remember the price though

have you verified that the heating elements are not there or are you just guessing?

Well... I haven't actually taken a seat apart to look for the bum warmers but can it be logical for Mini to put the heater in the seat if the car isn't ordered with that option? Highly doubtful...

on the other hand, it might be cheaper just to make them all the same way.

Partially true--------, If the battery NEG is not disconnected while the seat connector is unplugged, then you will get the non resettable airbag alarm. Ignition does not need to be off.

This seems to be the trend with several upgrades. For example I bought my MINI Cooper 2005 used and it did not have the computer upgrade that gives you mpg readouts ect... I did however have the stalk and the temp gauge already installed. All it took was a computer update at the MINI dealer for me to have the full computer features. I have heard the same for heated mirrors just needing final wiring/buttons installed and a computer update. I think I have also heard this is true for the heated seats, everything except the switch (which goes on either side of the mirror adjustment knob) and the computer programing are installed. When you buy the package you are paying for the "rights" to use it I guess.

It would be worth looking into and something I would really like to have. This is the problem with buying used MINIs, you can't pick some of the factory upgrades and it cost much more to do it after the fact than it does when you order it to just do the upgrade. I really really wish the person who ordered my MIN originally had opted for the multi-function wheel...