Actually, yes, it will, which is why I set my site up like this:
will load the DirectoryIndex (set via .htaccess) file home.php, which is a brief introduction to what is on my site.
Dropping the www. is also forbidden, as domain.com and www.domain.com
are two different sites, so far as search engines are concerned.
The reasoning for this is that search engines index sites based on the URL, not upon the uniqueness of content--i.e., two sites could be identical, but if they have different URLs, they are considered different pages.
If you have people linking to your site in two different ways, your PageRank and search engine status will be split between the pages, which doesn't do much for rank and results. Better to encourage a standard way of accessing your page to prevent this.