Difference between っての名詞 and る名詞

Question

In the grammar explanation for なりに on japanesetest4you.com, I ran into the following sentence:

私には私なりの理由があっての事だったんです。

I am curious about one part in particular:

があっての

Is this any different than がある? I know の makes it so that あって describes the following noun instead of the following verb, but why not just use がある instead — which already modifies a noun by default?

The one reason I can think of for using があっての is in conversation when the speaker is not yet sure what they will say next and needs to tie the って to a noun. But I am unsure if this would be the main for using or if this would work with every verb.

Answer 1

あっての emphasizes the prior phrase as a reason, without which the following phrase could not be. Please see here for other examples

がある would not make much sense here as a modifier of こと。You could say 私には私なりの理由があったんです, but it is not as strong an utterance.

Answer 2

The following four sentences are all grammatical. I would like to discuss these only in this context.

1. 私には私なりの理由があってのことだったんです。
2. 私には私なりの理由があってのことだったんです。
3. 私には私なりの理由があってのことだったのです。
4. 私には私なりの理由があることだったのです。

It can safely be said that sentences 1 and 2 are usually heard in conversation because of ん, not of あって, but 3 and 4 are a little more formal, which can be used in spoken and written Japanese. But it seems very difficult to find slight difference between 3 and 4. In the sentence 4, the speaker (私) is fully aware of his own reason, while the sentences 1, 2 & 3 having あっての may imply that even if the hearer may not know his reason, he has his own reason. The use of a little indirect expression あっての might make the speaker avoid criticism or something from the hearer. This is my opinion or feeling, but others may feel in other ways.