A couple of people, cwebber and Rodrigo have (comparatively recently) switched to using StumpWM as their primary window managers. Perhaps there are more outside of the circle of people I watch but it's happened enough to get me to think about what constitutes software minimalism.
While StumpWM is a minimal program in terms of design and function; however, in terms of ram usage or binary size, it's not particularly lightweight. Because of the way Common Lisp works, "binaries" and RAM footprint is in the range of 30-40 megs. Not big by contemporary standards, but the really lightweight window managers can get by with far less RAM.
In some senses this is entirely theoretical: even a few years ago, it wasn't uncommon for desktop systems to have only a gig of ram, so the differences would hardly have been noticeable. Now? Much less so. Until 2006 or so, RAM was the most performance effecting limited resource on desktop system, since then, even laptops have more than enough for all uses. Although Firefox challenges this daily.
Regardless, while there may be some link between binary size and minimalism, I think it's probably harmful to reduce minimalism and simplicity to what amounts to an implementation detail. Let's think about minimalism more complexly. For example:
Write a simple (enough) script in Python/Perl and C. It should scan a file system and change the permissions of files such that they match the permissions of the enclosing folder, but not change the permissions of a folder if it's different from it's parent. Think of it as "chmod -R" except from the bottom up. This is a conceptually simple task and it wouldn't be too hard to implement, but I'm not aware of any tool that does this and it's not exactly trivial (to implement or in terms of its resource requirements.)
While the C program will be much more "lightweight," and use less RAM during while running, the chances are that the Python/Perl version will be easier to understand and use much more straightforward logic. The Python/Perl version will probably take longer to run and there will be some greater overhead for the Python/Perl runtime. Is the C version more minimal because it uses more RAM? Is the Perl/Python program more minimal because it's interface and design is more streamlined, simple and easier to use?
I'm not sure what the answer is, but lets add the following factor to our analysis: does the "internal" design and architecture of software affect the minimalism or maximalism of the software?
I think the answer is clearly yes, qualified by "it depends" and "probably not as much as you'd think initially." As a corollary as computing power increases the importance of minimalist implementations matters less generally, but more in cases of extremely large scale which are always already edge cases.
Returning for a moment to the question of the window manager, in this case I think it's pretty clear: StumpWM is among the most minimal window managers around, even though it's RAM footprint is pretty big. But I'd love to hear your thoughts on this specifically, or technological minimalism generally.