As I have mentioned numerous times your current package is biased towards Apache/Apache compatible httpd(s)
me wrote: It is important to be clear that the goal is to develop an application that will install and run equally well on any specified web server environment, with no application component or design favoring one web server environment over another.
Adding IIS configuration files is fine, so long as they are not active by default and merely available options that can be renamed should it be appropriate for the server environment. The same holds true for .htaccess files, they should not be distributed as .htaccess but instead as htaccess.txt or htaccess.conf, anything other than live configuration files at the time of upload/install. As has been proven time and time again in the support forum, distributing live configuration files in the wrong or unsupported environment wreaks havoc. More and more web hosts are locking down distributed configurations and using global directives instead. Neither .htaccess or web.config directives will work on servers where allow override is off.
Since neither configuration type is required to secure a phpBB installation, that makes providing them optional rather than mandatory which clearly supports distributing them as optional files rather than out of the box ready.