I know I tend to freeze up when writing whiteboard code in front of a interviewer, so I do not want to subject somebody to that when I am interviewing. When you are looking over someone's shoulder, you are not getting a true picture of their ability.
The other thing is that writing code on a whiteboard has nothing to do with coding in the real world. You write some code, test by running in a browser, command line or IDE, refactor, test again etc. Expecting someone to write perfect code without running said code is ridiculous.
Whiteboards should be used for sketching out ideas, i.e. architecting different ways to solve a high level problem, like how should I organize these objects in the application? What should the interface look like?
That said I feel like interviewing is important enough that a large company with (presumably) large resources ought to be able to make sure a laptop is always there. But it isn't as simple as "just bring a laptop", you'd have to have an enforced process.