I think what the Macmall guy meant was, that a macbook pro is better suited as a desktop replacement mainly because it has a bigger screen, and a couple more expansion ports.
If you're contemplating between a a 2.4ghz MB and a 2.4ghz MBPro, then you've only got 2 questions to ask yourself.
1) Do you need a discrete graphics processor? That is the biggest advantage a MBPro has over the MB. If you plan on playing any video games, or hooking it up to any monitors larger than 22" then you might want the Pro.
2) When you're on the go, do you prefer a 13" or 15" screen?
Other than the above, as long as you don't require Firewire, i think you're alright with either one.
PS - That quip about 22" monitors only applies to computer monitors, not TVs, because computer monitors above 22" run at 1920x1200 resolution or higher and you'll need the Pro's discrete graphics to run HD movies at that resolution.
This is what I was about to point out about the MacBook Pro recommendation. The MacBook Pro has a bigger screen, and a slightly higher resolution, which might be more comfortable for you to use for long periods of time (and is it just me, or is the aluminum macbook pro's display brighter and more vivid than the aluminum macbook's display?).
You mentioned you would use an external display along with an external keyboard and mouse, in that case, the MacBook would suit you fine. I have the white MacBook and use it as my only computer, I try to take care of it but I don't "baby" it, it keeps going in and out of my backpack going back and forth to school, library, class lectures, around my university they have wifi everywhere, which is good news for me and bad news for my macbook

. The Aluminum MacBook feels even sturdier than mine, while weighting less, which would make it more comfortable to carry around. The MacBook Pro also weights more.
As I'm sure you've been told before, if you dont do any intensive video editing or use graphics intensive applications (ex. gaming), the MacBook is a nice alternative, since it can handle most tasks without breaking a sweat, even some light gaming.
Check out the refurb section on the apple website as well, they have some pretty decent discounts on certain models.