I would like to dispute that claim. I do work on both Windows and OS X every single day, or rather my PC deals with projection for teaching other PC users. Most of my work couldn't even be done on a PC, its core and reaction time is simply too sloppy. My DJ equipment alone is all the proof needed. Top notch PC, with nVidia GeForce 660M GT graphics card, 4 Core Intel i7 and 8 GB of RAM and my DJ software lags, old 2009 MacBook White with an Intel Core 2 Duo and 2 GB Ram and a nVidia GeForce 9400M runs smooth (Serato DJ, Traktor Pro 2 and Virtual DJ testet).
Word vs. Pages is easy in my case, Pages wins thanks to its handling of graphics elements and easy to use layout system.
Excel vs. Numbers is no contest for my needs. Excel is in my opinion the ugliest spreadsheet around, and I need to create smart columns and rows manually, where numbers often do if for me automatically. Makes formulas so much easier.
PowerPoint vs. Keynote, there is just no comparison. Period.
And thats just a small amount of what I use my Mac for, both at home and AT WORK.
If you feel it can't be used for work, then maybe you shouldn't claim its hopeless at it, it is just YOUR opinion, and I don't think many in there share it.