Maybe it's just me, but almost every office I've visited in the past 8 years has been mostly laptop-driven for 99% of their staff.
Do you mind telling what industry you work in, that you a) use a desktop and b) aren't afforded a laptop as well?
Obviously, there are ways around all of those situations. I can email my slides to the presentation machines in the conference rooms, etc. But they don't really beat the convenience of just grabbing the computer I used to make the ppt and knowing that everything will work. Sometimes I get quite jealous of colleagues with laptops.
And then, of course, there are the aforementioned cases of travel or wanting to work from home instead of coming in.