The time and difficulty are the prices for a truly open process. Defacto standards are often technologically more sophisticated and come to market faster than formal standards. Unfortunately, everyone pays a price for the monopoly sometimes gained by the holder of the defacto standard. One other important difference between defacto and formal standards is in the area of conformance testing. The conformance tests themselves are performed by an accredited neutral party.
True interoperability can happen only when conforming implementations of a standard exist.
Defacto graphic standards such as TIFF and PICT exist in dozens of slightly different variations. My TIFF file won't necessarily be usable by your software that supposedly reads TIFF files. Formal standards implemented by conforming systems are the best way to guarantee interoperable functionality. Aside from its inherently open nature, the real clout of a formal standard comes from its use in procurement specifications. Of course, defacto standards could be used for a procurement specification, but formal standards provide a more competitive open basis for the procurement.