The notion that because the ECU has electricity flowing through it during normal functioning somehow causes wear and tear is surely laughable isn't it!? Especially after just 44K miles!
I suspect your ECU problem was nothing to do with 'wear & tear' as such, but the ECU being unprotected internally against an external short circuit caused by the dead injector. What they are really saying is "it's nearly 10 years old, you've had your money's worth."
Stand by for a bit of waffle, but there is a serious point to it at the end.
There are a few problems that particularly afflict modern electronics as they age. Certain components deteriorate with age, and loads of cheap electronics have been manufactured using poor quality capacitors - up until very recently, there was an epidemic of cheap TVs failing after 18-36 months due to junk power supply capacitors. On this score, things have improved a bit.
The other thing that has caused problems is the introduction of lead free solder. It's prone to dry joints where heat cycling is involved, and in older equipment, weirdly grows conductive crystalline threads, causing short circuits. The fix in both cases is to remove it and re-solder with good old fashioned leaded solder.
That's progress for you.
Now comes the punchline. In ten years time, when people like us are looking at buying secondhand hybrid and electric cars, the electronics in these will be approaching the point when the problems start piling up. Even before you consider the batteries, the electronics are so complex, repairs will soon become uneconomic.
