Rogers points to James E. Robinson III, who explains why specs matter:

I used to think there was a virtue in less precise, more readable specs because they are much less intimidating to new implementers of a format. The success of XML-RPC has been driven in part by how easy the spec is to understand at first read.

But making software interoperate well is a hard job that becomes significantly harder when a spec lacks precision. An incredible amount of time can be burned on arguments over interpretation, especially when a programmer is told that his code doesn't meet a spec.

I came around to that point of view as well - interop is actively harmed by loose specs - regardless of the prominence of people who think otherwise.