I think you have slightly misunderstood the definition of
overclocking.
From Answers.com:
Overclock
To speed up the computer beyond the manufacturer's
specifications in order to run faster. This is
accomplished by changing a jumper on the motherboard or by changing
the clock crystal. The motherboard and CPU may or may not be able
to handle the increased speed. Enhanced cooling systems are
typically added when a CPU is overclocked. See mod, multiplier lock
and CPU cooler.
So when an Intel CPU leaves the factory specified as a 2.8 Ghz,
it is a 2.8 Ghz. Maybe it can be ran at 3.0 Ghz (that's where
overclocking comes in), but if Intel labels it as a 2.8, it's not
underclocking.
Same goes for AMD. Their CPUs are not overclocked in any way until
they reach the hands of the end-users. I'm rather curious where you
got that impression from.
Regarding the model number, I've posted a link in my previous post
about it. The number is there basically for ease of comparison when
choosing between an Intel and an AMD. If you choose to believe that
those numbers are faked to bring up sales, you can always google
for benchmarks done by others on those OC forums.