"For most professionals..."

Professional what? If you'd said, "For most people" I would have tended to agree and let things slide. But I think you've gone overboard attempting to paint the needs of all "professionals" with a single brush.

I could talk about the need for a larger screen, faster CPUs, RAM, multiple monitors, or ports, or graphics power, and then of course you'd backtrack and say (as you commented elsewhere), that yes, if you need some or all of those things then by all means buy the MBP.

But each one of those people whittles away at "most", to the point where I think your argument starts to fall apart.

Further, your core argument simply comes down to the price differential and, as others have also mentioned, "most" people (including professionals) tend to keep their Macs around for awhile. And so if you amortize those costs over time I don't think an extra $10/month is going to sway most of them.

Which in fact leads to the final point, as I'd say that most people who use their machine for "professional" work understand the value of their time vs. the cost of their equipment, and anything that speeds up their workflow is probably worth its weight in gold... or at least an extra $500 or so.