R2RML - SQL string representations

The R2RML spec [1] has language in section 10.3, that prescribes the
mapping of SQL string values to plain literals. This surprises me, I would
expect SQL strings to map to XSD strings. My understanding is that the RDF
group is moving away from plain literals. What do you think of changing
this to map SQL strings to XSD strings?

Thanks.
-David

[1] - http://www.w3.org/2001/sw/rdb2rdf/r2rml/#datatype-conversions