This is pretty confusing for new folks kicking the foundation tires. Your example on original download will start breaking upon uncommenting the following:

//$row-width: rem-calc(1000);

why would you make this different then the provided example? Out of the box your example uses these values:

row {
width: 100%;
margin-left: auto;
margin-right: auto;
margin-top: 0;
margin-bottom: 0;
max-width: 62.5rem;
*zoom: 1;
}

Shouldn't the default uncommented value be this?:
//$row-width: 62.5rem;

That way your example doesn't automatically break when you uncomment that setting in the settings file. Inconsistencies like this makes things a bit confusing....