It is never obvious who is really important. There are the troubleshooters, as you say, and also the coordinators. They are not really management, not really developers, not really sales. No one really knows what their job is but remove them and things stop working.
Laying off people may have unintended ripple effects too. The not-so-productive guy you let go may be very good friends with your best engineers, and he may take them with him as he gets hired by a competitor.
The best employees are the ones who can quit the most easily, as they will have no problem finding another job. In fact, the reason they are working for a company may just be because they are comfortable in there and don't bother looking elsewhere. Shaking things up too much may just be the motivation they need to find something better.
This would be particularly on Torvalds' mind, I assume; people who fix bugs in the Linux kernel (generally not a lot of lines of code) are generally more valuable to the project than people who contribute device drivers for obscure hardware (many lines, much productive, wow!)