NetBSD is very different than GNU/Linux when it comes to updates because the whole OS is the same version for all supported architectures. GNU/Linux, conversely, has very few distros which support more than a few architectures, and even Debian has trouble keeping m68k up to date. That's not to say they're not working on it, but you can't install a modern Debian right now. People are working on the toolchain to get things up to date presently.
NetBSD's advantage is that the same source code tree is used for all architectures, so all of userland is exactly the same for amd64 as it is for m68k and VAX, for instance. The toolchain is the same version, all of the daemons are the same, et cetera. By not keeping them separate, all the architectures benefit, plus you know if your code runs cleanly on VAX, m68k, Alpha, SPARC, et cetera, then you know it's good, portable code.
NetBSD's pkgsrc is also architecture agnostic as much as it can. You'll never hear pkgsrc developers say something like, "m68k? Who uses that? We don't care about fixing that." I've heard that many other places, though, even though everyone should care about making their code as correct as they can. After all, there were tons of x86 developers who didn't care about correct code who had to go back and fix tons of things when they wanted their code to work on 64 bit x86. Some people never learn.
To summarize, NetBSD is up to date and well supported on Amiga.