Agreed, to an extent
There are certain niche (for relative values of "niche") products that aren't available for Linux (not just Ubuntu). You will not see Visio (or any MS product) run native on Linux. Although there is Crossover Office (or whatever it's called), and various "tricks" to getting MS Office to run under WINE (I've had no luck with them personally - OpenOffice does everything I need).
Photoshop is another. Yeah, GIMP is good, but why learn a whole new program (which may or may not do the right things) simply to switch OS? AutoCAD is another one.
Many games run under WINE (C.o.D may be one, I dunno, I am not a big gamer). Native Linux games are growing (Steam seems to be coming to Linux) but it will be a few years yet before Linux truly competes with Windows as a gaming platform.
One option, if you like Linux enough but can't give up a few Windows apps, is to switch to Linux and then run WINE (for the that work under WINE) and host a virtual Windows box in VirtualBox. But if Windows is the only thing that scratches your itch completely, then use Windows; no shame in that.
My main OS is still Windows XP. When that gets too long in the tooth (and that time is fast approaching) I will switch to Linux 100%. I doubt Windows 7 has support for my hardware and, quite frankly, I don't want to blow £200+ just to be able to watch TV (amongst other things). I'll just install Myth and go from there.
I run Linux on all my laptops - it's awesome there. Way better (and more stable) than Windows ever was.