I'm sure they're made harder to maintain to drive people back to main dealers and their extortionate prices, although they do have high costs and expensive commitments. I recently had a local truck main dealer tell me that they struggle with certain faults, so if they struggle how is an independent expected to cope let alone a diyer.
Emissions and higher mpg are the major driving forces for making things complicated engine wise. As chunkers mentions space is lacking in the engine bay making it very difficult to work on, specialist tools are often needed. Even for brakes you may need specialist tools to wind back the calipers on some vehicles. Even changing headlight bulbs is ridiculously hard on a lot of vehicles now, although with HID lamps and leds we're moving away from that.
Fortunately I don't get to involved with cars, but trucks/vans are going the same way. I do wonder what the future holds with regards to owning vehicles. We had a 2010 Skoda a couple of years back which had gearbox problems, we spent a couple of grand fixing it and that doesn't take into account our labour. Also an 09 BMW which was a nightmare, it would run fine then not run at all. Our diagnostic system didn't really show anything, our local diagnostic guy didn't have a glue either, so it went to BMW. They seemed pretty clueless but thought the engine was now damaged, so I found an independent BMW specialist, he confirmed the engine was shot - completely flooded with diesel in the sump and exhaust system. We sourced a second hand engine and he fitted that. Trouble was no one could tell why the injectors had dumped so much fuel in the engine, was it the high pressure pump or something else such as the ECU over fuelling - would the same happen to the replacement engine? IIRC even the ECU was changed from the doner vehicle . Fortunately the car was OK after that, but the overall bill came to 4 or 5k, possibly more. Point being your average punter who runs an old car can't afford these sizes of bills (both these were our own company cars) and I can only see this sort of occurance becoming more common as vehicles get more technical. Both those cars were around the 100,000 mile mark, our company cars are now leased.
Electric cars are even more complicated, I'd hate to think how much a set of batteries will cost, they'll probably last just long enough for the car to get into the second hand market at 3 to 5 years old and then give up
On a positive note when things go well I think they are generally more reliable and lasting longer.