It's a matter of context. XFCE is usually shipped as a lightweight yet highly configurable alternative to the feature-rich desktop environments (DE) such as KDE and GNOME. Which it is. But that's only relative to the resources that it's peers consume. However in the last 5 or 6 years LXDE has come on the scene - which is even even more stripped down than XFCE was and as LXDE has a strong focus on modularization, it's even easier to run a low-footprint LXDE desktop. But as it's a relatively recent DE, it's not been a distro default-choice until recently.

There's also E17 (enlightenment) which has been around for donkey's years yet oddly seems to draw very little attention despite it's impressive performance. Not sure why that is, but if I had to guess - it might be because it's aesthetics is a little more individual so switching between different toolkits in E17 can be a touch more jarring and harder to unify.

However if you want really low footprint, then you need to run purely window manager instead of a full desktop environment. But they're less intuitive, less pretty and just generally another class of UI.

So there's a reason why XFCE is (or was) the low footprint DE of choice.

> "Maybe we can say the netbook was second generation then. It was an Acer Aspire One. I think you could choose between a weird crippled Linux or a Windows install. Or maybe it was dual-boot? I installed a fresh copy to get rid of the crapware anyway."

You might have a 1st generation Acer netbook then. But Acer weren't the first to market with netbooks. I think they were a full year behind ASUS's EeePCs (and even further behind similar devices aimed at different markets - such as the OLPC).