Key points are not available for this paper at this time.
Traditional readability concerns are alive and well, but subsumed within several more recent documentation quality efforts. For example, concerns with interestingness and translatability for global markets, with audience analysis and task sufficiency, and with reader appropriateness of technical text all involve readability, but often in ways not easily measured by any formula.
Gretchen Hargis (Tue,) studied this question.