If you don't want to read the whole thing, my ultimate conclusion is
It is all digital anyway, but it could have equally well been displayed with an old fashioned mechanical needle. An LCD is cheaper and have fewer moving parts and is apparently sexier, so that is what they did.
Here is why.
The Lexus marketing speak for the LFA is at http://www.lexus.ie/range/lfa/features.aspx (make sure
Features is selected and click on the
performance cockpit item and look at the middle of the second paragraph after the picture.)
"The central tachometer runs to 10,000rpm and features a fast reacting LCD needle designed to exactly replicate the V10 engine’s insatiable appetite for revs."
So, the display is driven by a computer that shows something that looks like a classic analog needle on an LCD display.
This display is most likely driven by the sensors in the engine that knows the speed of rotation of the crankshaft to some ridiculous level of precision. That is, ridiculous if its only purpose was to display the engines RPM. In fact, the RPM is an almost an incidental piece of data from the high resolution sensors measuring the angle of the crankshaft at any given moment in time so that the precise timing of the ignition system can be delivered.
For a V10 at 10,000 RPM, the need for exact and timely data is a real design challenge. A rough guess is that it measures the angle at least a thousand times per rotation, so my guess is that it knows the speed and position of the crankshaft around 170,000 times a second. I'm probably grossly underestimating the precision as I don't know the actual details for this car.
Now and then — maybe a few hundred times a second, maybe more — the RPM information is feed onto the main digital bus in the car (probably a standard CAN bus). The data is then received by the computer responsible for painting the LCD display of the tachometer, updating it at perhaps one or two hundred times a second. This is far faster than the human eye can follow, so much greater speed would be useless.
Could this be done with a mechanical needle looking just like similar displays have done for maybe a 100 years? Yes of course. The needle would probably be driven by a medium fast servo system and its own little micro controller. Even though it was a mechanical "analog" needle, it would still be digital in that it showed an approximation of the digital value from the CAN bus.