I don't know. No (cheap + good enough) mp3 player ever took over the iPod.
There are always exceptions to the rule. The success of the iPod in the face of fierce competition will be studied in depth in B-schools for the next 50 years. But in general, people are more willing to pay less for good enough features than to pay more for slightly better. That's why there are a bazillion Honda Accords and Toyota Camerys on the road, and far fewer cars that cost over $35k even if they are "better". Or why most homes have a GE sub-$400 Washing Machine instead of a $1200 LG. These things are "good enough" and cheaper.
But I'll freely admit that the iPad has taken off far more strongly than I think anybody would have expected. It may have hit that critical mass the way the iPod did as well and nothing will be able to break that.
would I rather drive a brand new BMW or a brand new toyota? while they are new, sure, I'll take the BMW. But speaking as someone who has owned an out of warranty BMW, well, after the warranty period is over, the Toyota is a better car.
Even if they were looking at how many were repaired (where lower retained value could tilt repair percentage downward, by making people disinclined to repair them, as you suggest) this would merely make other brands of laptops less reliable (with lower numbers caused by fewer damaged laptops being repaired); correcting for it wouldn't improve Mac/IBM/Lenovo's numbers, though it could damage the others, making them seem better by comparison.
Bad example since the more expensive cars usually aren't better. They tend to break down more often and be expensive to get fixed.