Agree, most of the time external drives are cases with USB/eSATA adapters and an "internal" hard drive. The only difference with a PC is that it's easier to drop the external drive.
That was correct ten years ago.
Nowadays the external drives of course contain 3.5" or 2.5" hard drives. But the inbuilt hard discs come with little or no warrenty, are "eco"-drives that are meant to be used only occasionally (not 24x7) and spin with only 5400 rpm.
Internal hard drives for personal/business (desktop, notebook) come with up to 4 or 5 years warrenty and spin with 7200 or 11000 rpm and have a better internal cache.
You know you can buy the external versions of those 7200 and higher RPM drives, right?
And that contrary to what you said, tons of personal/business laptops come with 5400 HDs. Not much quality HD on a €400 euro laptop or even some Apple models.
Citation needed.
There's no reason for the external drive to "die before the laptops internal one".
Not only that: you can actually buy the very same drives that are in your laptop for external use if you like.