Hmm... are you sure these are correct? MegaGlest should be fine with less RAM, and I've heard of others playing so, though quality may suffer. And original Glest only need OpenGL 1.3+, what does MG add that needs a slightly newer version? And why is multiple cores *required*? Wouldn't these all be recommendations (except perhaps the OpenGL requirement). You'd also need a sound card that supports OpenAL.
As for software, Mac and FreeBSD are also supported, and I imagine any OS that you can build the prerequisites on, MG should compile on.
RAM:1 GB is really not much, I'm referring to total system memory. The operating system and background tasks will also eat a non-neglectable share of RAM. You may be able to play some configurations with just 500 MB total RAM, but if you crash with an error in case you setup or join a multi-player game which has too big maps or too many players or complex tilesets or whatever then things are really getting out of hand. We don't want this to happen, especially not people joining multi-player games with crappy hardware. Lowering the requirements here would just give a wrong overall impression on what is needed. As always, people with lesser RAM can always try their luck.
OpenGL:The original requirements description for vanilla Glest should still hold true. You are not quoting it entirely correctly, though, since it is actually OpenGL 1.3 and some GL/ARB extension (I don't recall which exactly, but it's in the MG READMEs/docs we shpo with the release, feel free to look it up). Instead of stating this, stating that OpenGL 1.4 is the minimum requirement makes things easier. As always, people with lesser OpenGL versions (those hardly exist nowadays) can always try their luck.
CPU:I listed multi-core as a requirement since this basically says you need a CPU which is not stone age and provides a certain number of BogoMIPS. In the past it was possible to compare CPUs on similar or same architectures by their operating frequency (as measured in MHz/GHz). This is no longer adequate for a while now. A better comparison scheme is BogoMIPS, but most people (including me) are not used to comparing (or even knowing these values) CPUs based on this unit. As such, I was looking for a readily understandable way to put it. Most somewhat-recent CPUs which provide sufficient power to run MG are multi-core CPUs. And so I came up with this. You are welcome to provide something better and evenly simple.
OpenAL:Thanks for the hint, this was indeed missing.
OS X + FreeBSD:Those are not supported by the MegaGlest developers. I am aware (and appreciate) that MG 3.4.0 is supported on FreeBSD by the FreeBSD community, but this is both different people (so we cannot, per se, make guarantees on continued support, and it is a different version than this requirements list is made for, which is 3.5.0+). I am also aware that there are readily-installable MG 3.4.0 (not 3.5.0, though) builds which work (more or less) on OS X. These are, however, not supported by the MegaGlest developers themselves (as discussed and for reasons discussed before) at this time. So, to date, the MegaGlest developers can really only declare to support the Linux and Windows builds, namely the ones they release themselves. Of course ,they will continue to support any community efforts to port MG to other platforms.