Why do I have to install apache2-utils when installing node.js?

The name apache2-utils is misleading. It is not a part of the Apache server. Apache just depends on stuff that you can find in this package. As it turns out, the compiler (or node itself) depends on the same utilities.

This means, that after the compilation and installation of node apache2-utils can be safely removed via sudo apt-get remove apache-2utils. This applies to the other packages aswell. However I don't recommend removing any of the packages. You will likely want to recompile node as soon as there's a new version.

tl;dr You're doing nothing wrong, when installing apache2-utils. It is a package of utilities, needed for compiling node. You can remove it after compilation.