Two things:
1) how do you establish that apple's internals are of mediocre quality? Where do you get this information? I'm not saying that Apple is great or worse, I'm just curious what the truth behind apple's internal build quality is.
I didn't say mediocre (that would be a G4), I said average. Average is fine, mediocre sucks. They have gotten progressively better on their components... Minus a few exceptions, and yes there have been some problems in recent years.
Besides experience (plenty), I pay attention to industry reports. Deal with enough computers you see trends, but also, if you work in the industry, especially when you are making recommendations for businesses, you need to follow this stuff. I tear things apart and look at tear downs to know what's in them.
Going back to Apple, it was well known they used low grade memory (a decent brand but a generation behind what was current speed) and while the dvd drives they used were high tech, they were problematic. Chips inside were also of average quality, they didn't always use the latest chipset, or the fastest, but it was solid. It's not a problem, but it's not what you expected considering the price.
As for today..
The most frequent failure on a computer was the DVD drive, followed by the hard drive, distantly followed by either the backlight or the fan. How many of those are in your computer? Apple was one of the first to ditch the DVD (their drives were notorious for failures) and also one of the first to ditch spinning drives. So why would a Mac be far more reliable than a cheap Acer? It lacks the two most common failure points. Not to mention, you are comparing a $1200-$2500 laptop, with one that probably cost around $300. It's not a fair competition when the average PC notebook is half the price and designed to last 2 years.
Give me an equal dollar Lenovo, older Sony (they sold their laptop division), Toshiba, heck, even an equal value Dell or HP of equal class*, and I guarantee you the results will be far different.
*I'll explain in a second
I see your point that you would, theoretically, be more careful with your $$$ laptop than with your average PC laptop. But that's, again, the outside. From my experience, PC laptops are EXTREMELY unreliable and I've had many in the 1200-2000$ range, which drove me eventually to Apple.
Now on to Apple: 3 macbook airs around me (1 GF, 2 of my friends), all 3-5 years old and still run perfectly. Even batter is OK.
Here is what most people don't undertsand with computers, particularly notebooks, there are classes to them. At the low end you have the home computer, these are usually your cheap Dells, HP, Acer, etc... By design these are only engineered to last 2-3 years under normal use, that's it. From there you have small business class/prosumer, these are engineered for a bit more durability and are meant to go 3-5 years, next is corporate level, these are meant to be easily serviceable, durable and reliable, they may not always look great, but they are expected to go 5-10 years (Lenovo X and T series dominate this class). Finally you get the executive class, this is where you get your Lenovo Carbon, Sony carbon edition, Apple Macbook Pro and such. These are the more exotics, they look better, are lighter and have nicer features, but they may or may not be any more reliable or have better components than the small business class.
Prices can jump all over. You can spend $1400 and get a home computer, and there are small business/corporate models in the $500 range, or you can spend $3000 and sometimes you get all of these at all of these prices from a single company. Executive systems typically start around $1200 and the sky is the limit, but their reliability is all over the board. All can have the same processors and memory. The corporate will most likely look the most bland, while the home system could be the flashiest and appear to have the most features. This is why you see an Acer with a Core I5 that costs $600, and then you look over and see an ugly Lenovo with an I5 and less memory for $1400. If you don't know any better you think the person is foolish buying they $1400 model. The $600 machine will probably not last as long, has a cheap display, touchpad and keyboard. And yet, you might get a Toshiba on sale for $800 that outlasts them both. It's completely unfair to compare a Macbook to a home pc, it's like comparing a a Kia to a Lexus but it's often what everyone does.
So where are all of these better pc's, well you don't usually find them at Best Buy because of what I said above. Try selling a $1400 Lenovo, a company the average Joe may have never heard of, when there is an HP or Acer sitting there that looks better, has the same specs and costs $350. He doesn't know about durability, what a good touchpad is like or how much better the screen is without them sitting side by side. He knows one looks better, has equal specs and dad or grandpa always had an HP.
Look, I'm not trying to trash Macs (other than their stupid single button and gesture BS), I actually respect them, but I recommend my customers follow the trend of who's giving you the best return on investment. Apple is (consistently) one of the most reliable on the market (these days), they look great and run well, and if you aren't sure which to go with, they are a safe bet, but that comes at a cost. I cant recommend a $1500 Mac to a small business when I know there are systems out there that give you 99% of the reliability, with Windows compatibility, for half the price (and is less likely to walk off). Mac is a luxury, not a necessity and for some businesses it can even be a liability. The world runs on Windows, sorry, it's true*.
*I'm not much of a Windows fan, but my customers need it.
