I suppose it's good that OSes such as NetBSD are available. Our philosophy is that portability is good for everyone - if you write good, correct code, it'll compile and run on all architectures, but if you only test on one architecture such as x86, you'll miss bugs and have issues due to assumptions; not only is there no reason to remove architectures, but there are very good reasons to keep them. As long as the toolchain is kept up to date and as long as a port has at least a few people checking it out now and then, we keep it.
We still support VAX, for instance. It keeps us honest - if the latest OS becomes unbearably slow on VAX for some reason, fixing it helps everyone.
One of the problems with GNU/Linux is that Linux (the kernel) is not designed to be portable - portability is often fixed as an afterthought. GNU (the OS) is pretty portable, but distros these days are often not volunteer groups with lofty goals - they're mostly businesses with a vested interest in having ways to distinguish themselves from other distros, so they're full of non-portable, gratuitously added code so they can add bullet points to their "feature" lists. There's no good reason, for instance, that the entire source tree for an entire distro can't be made to compile and run on a different architectures, particularly fast ones such as PowerPC, and especially distros which had recently had support for said architectures. It implies that someone recently introduced some poorly written gratuitous code since the last version.
