Skin string replacement happens in 2 places, not 1, and having just 1 place would be easier to manage.
/public_html/ccskins/shared/strings/*.php are the default strings.
/public_html/customsitename_files/skins/customsitename-skin/strings/customsitename.php
and
/public_html/customsitename_files/skins/customsitename-skin/strings.php
are where to declare replacements.
Some of ccHost respects one and some respects the other, so OFLB has duplicated the contents to be sure. Ideally there would only be one.
I'm moving this 'feature request' because this was done, in fact, "by design" - there are some strings (like "Skip to content") that are strictly for a specific skin and have no business in the globally shared 'string profile' - it's possible the better way to handle this would be to create template-tags (like those in 'admin/templatetags') which only the skin would understand.
Either way, we need a way for a skin to introduce it's own strings, particular to the way it presents things and not force every skin maker to put strings into the whatever the currently selected global string profile is.
This is by design (see comment above)