Here's an old thread with plenty opinions:
http://www.tomsguide.com/forum/81388-35-compare-dell-toshiba-asus
I can't find any evidence of the above statement "The funny thing about Dell is a lot of their OEM parts now are made by Asus".
Many of the parts are of course made by electronics manufacturers in Taiwan and China, just like every other computer component or consumer electronics item. Do some research on Foxconn and you'd be surprised how much of their stuff you have bought.
I've only ever used Dell laptops, because they are the only supplier for my company.
Batteries are the most common thing to fail of course just like every other brand. I've seen these fail after 12 months, but then the laptop I'm using now is four years old with no problems at all.
Other than that, the occasional failed power supply and cracked screens due to physical mis-handling are the only issues I've seen.
We still have 10 year old laptops kicking around the office for specific tasks.
Your post wasn't about which laptop to buy, but about relative quality.
I can see arguments against Dell on price certainly. Some of their spare parts are outrageously expensive.
On functionality too, there may be a manufacturer that makes a laptop to suit your specific needs perfectly.
In terms of quality though, I can't fault Dell at all.