It is, and it has become nuts.
A car engine is a very simple thing. Even the most complex is nothing that fancy. Granted a modern vehicle has more electrical components, it is now common for every car out there to have a controlling computer that is linked to most major parts via sensors so it knows when to illuminate the "Check Engine Light" and these sensors are from simple things like tire pressure to a little more complex like O2 levels in the exhaust to determine if the engine is burning the fuel correctly.
Take a four cylinder engine in its basic form, crank shaft link to the pistons housed in the combustion cylinders with two valves, one for injection, one for exhaust, timing is controlled by a cam shaft.
In the 80s they moved the cam shaft to above the valves, thus we have SOHC, single over head cam. Then came three valves per cylinder, two injection, one exhaust. Remove the carb and now we have electronic fuel injection, nothing very complicated here. A step further for performance boost, we can have, as is found in most I4 engines, is four valves per cylinder, the twin exhaust valves allow the injection to be given a form of forced induction, much like the effect a super charger has. To facilitate this, each bank of valves, the two injection and two exhaust valves, get their own cam shaft, thus DOHC, duel over head cam.
Now the new thing is to variate the timing of the cam even further with variable valve timing, again, not a complicated thing, it just took a while to build one that can last 30,000+ miles of usage, and some on the road still cannot meet this demand.
Connect the heat to a very simple air cooled radiator, have a air hose run over the block to get heated for cabin heating, run another air hose through an engine powered compressor to get A/c for the cabin. 4 bangers suck on horse so throw in a turbine to create further forced induction in the intake, and to keep things simple, power the turbine from the exhaust and we now have a turbo charger.
Slap an alternater to the crank to generate electrical power to help power the system and charge the battery, and there you have it.
The space shuttle on the other hand does not feed in outside air, it has self contained life support system. No need for an alternater, no, instead we have three fuel cells.
You seem to want to make out the SSMEs as being something some guy can build in his sheed if he so pleases, but yet we have three of them, fed from umbilical lines from an external fuel tank. Oh yes, and they are throttle-able rocket engines.
We also have two orbital manuvering pods, a slew of RMS jets on two systems, the pri and vern, 5 GPCs, a water system linked to the fuel cells, three forms of radiators, the payload bay loops, the flash evaps, and the ammonia boilers, the RMS, the camera system, all the attena, three GPS systems, the star trakers, the IMUs, the three APUs, the Helium pumps for the main propulsion system and the OMS, isolation valvues all over the darn place, rgas, radar altimeters, the MLS system, the air data probes (since it is also a plane remember), TWO O2 N2 systems for the cabin, an airlock, now the APDS, and a bathroom, just to name a few systems the Shuttle has.
After a successful mission, on which nothing went wrong, it takes thousands of people to turn around the vehicle, to check it out, and zero out the systems.
It takes one guy to look at a mass production car and fix it, and of course you only have him look at it after it breaks.
I would bet no aviator would ever think their aircraft is more complex than the Shuttle, even should it be a Boeing 777, let alone think his 4 cylinder auto.
I look at this list, and your VW looses. Shuttle is more complex. Period.
