David Rosenthal has a detailed and useful analysis of the value of open format specifications for preservation:
If we plot the quality achieved by a newly created renderer for a format against the cost of creating it we will get an S curve. A certain amount of money is needed to get to a barely functional renderer. Beyond that, quality increases rapidly at first but after a while the law of diminishing returns sets in. Getting from 99% to 99.9% is very expensive; the cost of getting to 100% is infinite. … It seems clear that preserving the specification for a format is unlikely to have any practical impact on the preservation of documents in that format. If, during the currency of the format, it acquires an open source renderer there is no significant risk of ever ending up without a functional renderer. The need for a new one to be created from the specification is extremely unlikely ever to arise. If that unlikely event ever happened, it is hard to believe that resources on the scale needed to do the job would be available. And in the unlikely event that they were, it is unreasonable to believe that the combination of the preserved specification and the available resources would be enough to create a renderer that would satisfy those who reject Open Office because of minor rendering flaws.
Don’t let the perfect be the enemy of the good.
Clearly, formats with open source renderers are, for all practical purposes, immune from format obsolescence. …