You probably mean the WHR-HP-G54 vs. WHR-G54S.
The WHR-HP-G54 is $10 more, but for people who need distance this is well-spent $10.
Why?
Regular Cable/DSL Router uses the chipset for RF Output; these chipsets are designed for an output of 30 to 40 mW.
Most Entry Level Cable/DSL Router emits 33mW.
With a 3rd party firmware you can "Over Clock" the out put of the chipset, however, since it was not designed from the get go for higher output you overclock the noise as well. The result is a stronger but Noisy signal.
Each one of the overclocked Wireless Routers has a "Sweet Spot".
As an Example, I have a Linksys WRT54G v4 that with 3rd party firmware it is OverClock to about 55mW output, beyond 55mW the output becomes too noisy, and there is No benefit from the additional power.
In comes the WHR-HP-G54 (the HP in the middle stands for High Power) the ?HP? has a build in RF amplifier post the chipset. The chipset provides to the Amplifier only 10mW.
I.e. the signal that gets to the amplifier is cleaner than the usual 33mW.
The Amplifier Boost this signal to around 100mW, the result is 100mW of clean 2.4GHz signal.
So, for $10 you get 3 times the regular signal and two times the functional OverClocked Signal. (Beware 2 or 3 times does not mean 2 or 3 times the distance).
Not a Bad Deal!
P.S. The WHR-G54S has an inside Heat sink, the WHR-HP-G54 does not.
Some people think that the WHR-G54S is better because of the Heat sink.
However, the chipset in the WHR-HP-G54 uses only 10mW of the 33mW, so it does not need a Heat sink.