It's really simple.

If a company's product requires a lot of support requests you do not blame the customer.

Ever hear the saying "The customer is always right!"

Anybody with their head in the right place (E.G. Not where the sun don't shine) should understand there is some kind of short coming with the documentation and/or installation possess. It doesn't matter if the instructions are 'out there' if the customer doesn't know that they need them, or where to find them.

Add an see more extra step to the installer.

Set up a simple RewriteRule using the .htaccess file in the install folder and 2 files. For example:

RewriteRule rewrite_test\.txt rewrite_works.txt

Then read the file:

$file = file_get_contents('http://yourhost.com/rewrite_test.txt');

If you get contents of rewrite_test.txt, mod_rewrite is not there.

Bonus points if rewrite_test.txt has a warning that mod_rewrite is not working, and includes directions/links on how to fix it.