Go ahead and do just this and let me know how it works out for you. Hell, do it on the carpet. If you have a hard drive, you will likely get the folder with a question mark (or is it exclamation point? I don't remember), indicating a bad hard drive. If you have an SSD this is a moot point, and would also be applicable to a Windows PC with the same setup.
I think the point he might have been going for, but of course I could be wrong, is that macbook pros (and that one generation of macbooks, I recall) have a better external build. The aluminum, I would think, can take a little more abuse than the plastic found on most laptops. I also don't get the warnings about HDDs. When I upgraded my PS3 HDD, my dad accidentally knocked the new HDD off a table (about 5 ft off the ground) onto solid tile, and it's never had any problems. My former coworker spilled water onto his macbook's keyboard. He was freaking out, but after letting it air dry for a couple of hours, it powered up just fine. I've never heard a story like this regarding an HP/Dell/Asus/whatever non-apple brand.
I actually just did a hard drive replacement for my brother's wife's Macbook, and it was a pain in the ass. It would've been easier if I had another Mac or probably even a working Linux machine, but flashing a USB thumb drive with a Snow Leopard image in Windows sucks.
Which could've been avoided if you had the original boot disk (or even a retail boot disk) handy. Not a problem with the computer, but rather a user error. This anecdote comes from someone who worked in a windows/linux/OSX repair shop for just a little under a year.
Long story short, any Mac after 2006 uses the same hardware as a PC. Macs ARE PCs. The RAM and hard drive are interchangeable between it and any given computer off the shelf (with the exception of the Air models). Logic board failures are uncommon, but also happen. I have seen a few dozen in the hundreds of Mac repair cases I've seen. I just don't get how people think Macs are somehow impervious to hardware failure. They can and do have hardware problems.
That's not entirely true regarding the RAM. If you don't use Apple RAM, you have an extremely high chance of the system not properly recognizing the RAM or using it at the appropriate clocking speed, as some RAM needs a little tweaking via the MoBo bios to get the clock speeds to work as advertised. You can't get to the BIOS on a Mac, at least not easily. I also find that the thermal compound in apple laptops (never opened an iMac or Mac Pro to check) is usually correctly applied, whereas I usually had to reapply the thermal compound in HP and Dell laptops because it was smeared on way too thick (and sometimes a hardened mess by the time I got to it). That's a subtle difference I've noticed between the two.
Also, and this is just a rumor asaik, apparently the new all-in-one iMacs won't recognize a lot of after market internal drives.
As long as your budget is $1,000+.
Which is about the standard price for all-in-one's similar to the iMac. The laptops are overpriced, however they do (or did, as I mentioned above, my iBook is still running strong after so many years) tend to have more longevity to them than other laptops, speaking from the numbers.
I could absolutely be wrong here, but I get the impression that most people defend their Macs because either A) it's the cool thing to do, or B) they have a natural inclination to justify their expensive piece of equipment. They're fine for what they are and if you're willing to pay the price, but they are nothing special and certainly not worth the price premium. I've been Mac; went back.
The same can be said regarding the confusion as to why people insist on berating people who own Macs (or any Apple product), either it's A) the cool thing to do, or B) a result of envy because others can't afford or simply don't own that particular piece of equipment. These days, you could argue that the newer computers are worth the premium price. After all, there aren't any other machines with the thunderbolt port currently on the market. What's to come of that venture, I honestly couldn't say; history could repeat itself and the lesser format can snuff out the powerhouse port, or we could see a shift in power, like what happened when blu-ray overtook HD-DVD.
For the record, before I get called an Apple fanboy, I use a linux box and an iBook as my main computers (when I need computers).