So if you are Mozilla and want your browser to get recompiled for Windows you might use such a service (I don't actually know whether Mozilla is doing this, just giving an idea)
AFAIK for OSX the only legal option is colocation - e.g. you provide an actual OSX machine, and it's installed for you somewhere for your use or your team (I'm actually not completely sure there).
I'm talking about OSX, since lots of these tools above are released for Windows and OSX, but not for Linux (yet).
Lack of choice to. Which sounds bad but can be good. For example Linux you have lots of webservers Apache. Nginx, tomcat all with different config methods.
Windows? Add the web server role, use iis and be done with it.
You can run Apache and Tomcat on windows if you so choose. You can even run nginx (albeit on top of Cygwin) [0].
You also don't need IIS to run HTTP endpoints. That said, IIS7+ is a pretty nice web server (I speak from experience as a shared web hoster ops and dev person). It's got a plethora of knobs and dials for tuning and is extensible (via native or managed code modules and handlers). But as always, horses for courses and all that.
IIS is great too and in-box. It's nice having smart defaults but a lot of options.