Unfortunately that quote from the manpage is at least misleading
System load averages is the average number of processes that are either in a runnable or uninterruptable state. A process in a runnable state is either using the CPU or waiting to use the CPU.
So far, so good.
A process in uninterruptable state is waiting for some I/O access, eg waiting for disk
s/is waiting/may be waiting/
This a major difference - especially in Linux where loadavg !== CPU load
. Processes can be made uninterruptable and left there for some (hopefully short) time. Two of these add 2 to the loadavg - but have NO
effect on CPU%. Apache is known to do this - likewise Oracle.
Then, of course, you also have tasks waiting on I/O completition which also contribute to loadavg as mentioned. So you have to understand the workload, and what processes actually are in uninterruptable wait.