Quality. ThinkPad, Apple, or some of Dell's premium lines won't break with life. This translates into:
- Mechanical build quality
- Choice of auxiliary components (wifi camera+chipset, etc.). If you're at a conference, you want to get connected and hook up to a projector reliably.
- Battery life
- Cooling
- Keyboard/pointer quality
- Size/weight
And so on. If you fly with a laptop once a week, whether the screws fall out from plane vibrations makes a difference.
One bad business trip, and you've covered the price delta of a half-dozen laptops. I'd never buy an over-speced, under-built laptop like the G5 SE. If my laptop is 15% slower, I care a lot less than if it's 15% more reliable.