At an average speed of 50mph, 2000 running hours comes out at 100000 miles. If the spec aims for all engines to last this long then you'd expect a good majority of them to last a lot longer. This doesnt seem too bad a goal to me.
It seems odd that you would accept a design lifetime that is 40% of a car made 13 years ago.
I'm also not clear why you would expect the majority to perform above spec? Wouldn't a significant number fail under spec? Isn't a care which may become a total loss in 60-80k miles basically tissue paper quality?
Personally, I think a pretty big swath of engines make it well past 100,000 miles now - there are usually other issues with cars at about the 10 to 15 year mark with most makes and models that have to do with rust.
Designing engines that last significantly longer on average (say 250,000 miles) would require either a beefier design, which will add weight and reduce efficiency, or exotic materials that will significantly increase the cost.
Automobiles are pretty amazing for what they are. I agree with many others that they have gotten ridiculously complex, but this is mostly because of the emissions requirements - and that said I do enjoy the fact that smog is not much of an issue (at least in the US) these days.