Can someone explain what rules for が come in play that make the sentence:
発売延期となっていたネットワークレコーダー「nasne(ナスネ)」の発売が8月30日に決定しました
grammatically correct? I would have formulated it 「nasne(ナスネ)」の発売が8月30日に決定されました, or to keep the usage of しました-form: ソニーは「nasne(ナスネ)」の発売を8月30日に決定しました
が simply marks a subject of a sentence, but your question is not really about the use of が.
Note that 決定する has two usages: 〈人〉が〈事〉を決定する (transitive) and 〈事〉が決定する (intransitive). The former usage is similar to 決める, whereas the latter usage is similar to 決まる.
When we say something was decided without a focus on who did it, it is more natural to use 決定する intransitively rather than using it transitively in the passive form or with a subject omitted.
There are other verbs which can be used as both transitive verbs and intransitive verbs. Examples are:
It is the nominative case marker on an intransitive subject. The verb 決定する can be used transitively as you expected, or intransitively. You may not be able to do this with the corresponding verb decide in English, but other verbs in English have the same type of transitive alternation.
The family settled in New York.
The professor settled the test tube on a stand.
