As a previous Software quality assurance engineer for a software company, I think that implementation of quality standards assures your customers that they receive consistent products under specifications.
Going back to your question it seems ISO/IEC 9126 was replaced by ISO 25010
http://en.wikipedia.org/wiki/ISO/IEC_9126
that http://webstore.iec.ch/preview/info_isoiec25010%7Bed1.0%7Den.pdf