Why do processes with higher priority to be allocated more timeslice?

Hi,

    It seems that Linux's scheduler tends to allocate longer timeslice
for processes with higher priority. Actually, the CFS scheduler which
is a new scheduler in Linux kernel also does the same thing. But, I
think this way does not fit with scheduler's principle.

    The goal chased by a scheduler is low latency and high thoughput.
Normally, a I/O-bound process has higher priority, while a CPU-bound
process has lower priority. So, a I/O-bound process (which has enough
timeslice) can preempt a CPU-bound process easily. This way ensures
lower latency. It is also necessary that CPU-bound processes are to be
allocated longer timeslice to improve throughput owing to less process
switch costs. That means lower priority processes (CPU-bound) should
be allocated longer timeslice, whichs obviously conflicts with the
actual practice taken by the Linux's scheduler. Any explanation?
Thanks.