When I look for "pro" features in a laptop, my list has:
- Docking station - so that taking the laptop from my home office to the work office is one-click detach, one-click attach (how "pro" is a mess of various cables for monitor, power, GbE, Kbd/Mouse, USB, ...)
- Removeable drive bay - so that I can have a second full-capacity battery, an optical drive, or a second 160 GB disk drive, depending on the task (and 90% of the time the second battery is in there - for 7-8 hours of real-life runtime
)
- Builtin a/b/g WiFi and 3G (EVDO/HSDPA) - for networking in the office, in the train, just about anywhere in a populated area
- Discrete graphics with 256 MiB plus of usable graphics memory
- Socketed CPU for easy upgrades (I've gone from Yonah to a Merom running 64-bit Vista)
- A case that strong enough to take a few bumps without denting and bending (magnesium-alloy, in my case)
My
Dell Latitude D620 has all that and more - in a package that is half a pounder lighter with a smaller footprint than an MBP 15".
Somehow, all these features are much more important than whether the MBP is ¼" thinner than the Dell (that's about 6.1mm, for those of you who don't live in the colonies).
- I think that Apple doesn't provide a docking connector or swappable drive bay for the same philosophical reason: they want a MBP to be self-contained and stand on its own, without a need for external devices for everyday use. At work I have a docking connector for my Thinkpad, but the ONLY thing it's really providing is my ethernet connection, and I could just as easily plug in the ethernet cable directly into the side of my Thinkpad. Personally, I don't WANT to switch the keyboard, mouse, and display that I'm using. I like the Thinkpads' and that's what I use. If I was using an MBP for work, I would have the same preference.
- Kudos to Dell for providing 3G connectivity as a BTO option already, but in the MBP world this functionality can be added through the Express/34 slot.
- 256 MB of VRAM *is* available on the MBPs, at least in the 2.33 GHz 15" and the 17" versions. Unfortunately, the "base" 15" MBP only has 128MB to increase the difference between the two 15" models. Stupid apple marketing tricks.
- Sorry, but socketable CPUs is not a "Pro" option, just a "you" option

The vast majority of "Pro" users don't consider the CPU upgradability of desktops, much less laptops.
- I would say the MBP cases are rather durable themselves, but the point is you're rather offbase in trying to argue that the Dell has superior engineering for durability/reliability than the MBP. Let me just list some features that are much more important:
* accelerometer to shut off hard drive in case of fall or rapid acceleration. I looked the Dell site and didn't see this for the Dells
* MagSafe adapter, which reduces the likelihood of an accident with the laptop, or of damaging the power socket itself (which would then only be fixed by replacing the motherboard
* in general fewer breakable parts (e.g. magnetic latch)
Let me put it this way: I still see a lot of Titanium PBs and almost never see ancient Dells from that same time period. And if anything the "durability" gap between Apple and Dell has only increased.
And finally, the Dell is smaller and lighter but only because it's 14" instead of 15.4". If you look at the 15.4" Latitude D820, it would be about 6.5 lbs., or almost a pound heavier than the 5.6 lb. MBP. Apple made the *strategic* decision that since "Pro" users of Macs tend to be more graphically oriented, that it's sweet spot was actually at the 15.4" level. And Apple *will* provide a smaller MBP, but it would be at 13" or smaller since 14" would be too close to the 15" models.