I haven't used IIS but one thing I can think of against it is that it has a completely different kind of url rewrite system than Apache. To me learning it doesn't make sense because hardly anyone in production uses Windows for hosting PHP applications so this knowledge is mostly useless. It's much more useful to use and learn rewrite systems that are actually used in production like those in Apache, Nginx, etc. That's why I prefer Apache.
In the same way I could say that I don't waste my time learning tools like puphet.com. I'm not saying they don't make sense but that setting up own environment can also work well. Certainly, there comes a point where features of such tools become handy and worthwhile but if someone doesn't have that many sites to host locally or doesn't need any non-standard installations then plain environment will work fine.
I have Apache, multiple versions of PHP, multiple database systems all installed by myself and they work very well. I use simple batch scripts to switch between PHP versions, different document root paths, switch on/off Xdebug, etc. and I keep all my local addresses in a separate Apache config file. Sure, learning all of this is not a 5 minute task but there's an advantage to it that this makes me learn configuring Apache and PHP and sometimes this knowledge comes in handy in other scenarios so this is not wasted time at all. Now when I need to set up this kind of environment from scratch I install all the components very quickly because I'm already familiar with the steps.