Except that's quite obviously not the case. You can use both GCC and Norcroft natively to produce programs. The advantage of cross-compiling with the GCCSDK is ease of use, especially when porting things from other platforms (even more so when they use the spawn of satan that is autoconf).
Take NetSurf, for example. As Peter rightly states in the article, it is generally compiled using GCCSDK on a linux machine. Why? Simplicity, above all else. I defy you to get a sensible autobuilder system working on RISC OS. However, just because the downloadable binaries are cross-compiled using GCCSDK doesn't imply that the developers themselves use this method. Certainly, some do (myself included, usually). Others compile it using GCC on RISC OS and it's equally possible to compile it using Norcroft on RISC OS (one developer at least regularly makes use of this method).