[RTTY] Question about NAQP rules

[Bill Turner]

Quoting from the NAQP rules:

"Use of external amplifiers capable of more than 100 W output is not
allowed."

I've been curious about that rule for a long time and just now getting
around to asking about it. 

If one has a high power amp and throttles it back to 100 W, what's the
difference?  Am I missing some subtlety here?

I can see where some ops might prefer to let their transceiver loaf
along and use an external amp to reach 100 W.  Why would this be
prohibited? This rule must have been inserted for a reason. 

Bill W6WRT