Explicitly, yeah, but any associative array using title strings as keys will automatically be case-sensitive, just because array lookups (and string comparisons generally) are case-sensitive. I have no idea how many of those there are scattered about.
Is there many of them - such things? The only one I found was LinkCache class. Parser, Linker, Title use only methods of LinkCache, when it's about Good|BadLinks. Maybe there are no other cases of use title string as keys of associative array?