>And for what purpose would it be nice?

I know you'll correct me if i'm wrong, but you seem to think the
*only* purpose of CPU speed is as a metric of overall system performance.
For which I agree CPU clock rate is not an accurate measure.

yes, sometimes people who dont know any better use it for that.

I can think of 3 plausible, legitimate uses without even blinking:

    a) mapping cycle-counter measurements of *real* code
       execution to wall time.
    b) calibrating use of cpu cycle-counter as NTP  clock source.
    c) ascertaining whether one of several externally-identical
       machines has been re-clocked or overclocked.
       say, in a lab.  These things happen...

I use the first 2 on mips.  (I need to recoutn delay slots in the
calibration loop that counts cycles between mcclock ticks: egcs
changed it. But if I leave it alone long enough, NTP will eventually
settle down and tell me the real numbers. :->)

so, if someone really does want to know the CPU clock rate for
something useful, why not let them? 

Arguing that `I dont see a legitimate use for this, thererefore you
cannot have any legitimate use for it'-- well, do we really want to be
that arrogant?

If you dont want it to be misused, fine, make it an option or something.