Licensing question about the GPL

[Steve]

	I'm involved in a discussion about the GPL and dual-licensing... 
situations like the Qt library where software is licensed under the GPL, 
but can be licensed for a fee under different terms for usage outside 
the parameters of the GPL.
        
	I've heard this used as a counterargument against the claim that GPL is 
a "viral" license (I don't use that term in a derogatory way, I thought 
that was the whole point to the GPL!).  However, the argument that I've 
heard states a copyright owner of GPL'ed software is able to 
dual-license that software, period.  Is that really the case, universally?

	What about if your software is GPL'ed because it includes other GPL'ed 
software?  It seems to me that in such a situation, you would be 
required to obtain alternate-licensing from that other software's 
copyright owner... who in turn would have to first obtain an alternate 
license for any GPL code that THEY had used, an so forth.  It doesn't 
seem logical to me that I could take the GCC codebase, make some 
changes, call it NCC ("New Compiler Collection"), and then dual-license 
it for proprietary use without first getting permission from Stallman or 
the FSF or whoever.

	Is my understanding incorrect, and one CAN dual-license any GPL'ed work 
(even a derived work)... or is it rather the case that you can only 
dual-license a GPL'ed work if you are the ORIGINAL copyright owner of 
all GPL'ed components (or have their permission)?