So.... the point of the examples is to demonstrate the spirit of the rules and what they are intended to address. There's significant human judgement that would go into a determination of violation of the current/future rules, which can look different in every situation. The point is not to set a hard limit, but to give a general feel for what is appropriate versus not. I would NOT take 20 as a hard limit either way - 5 or 10 planes could be considered inappropriate depending on the context of it. He had also stated with the rule change that it will be removed from the alliance section and put into the main section of rules as it's intended to apply to all players. Given that, I'll take a stab at responding - sami can correct me if I'm wrong :-).
1. Spirit of rules applies here, see above.
2. Spirit of rules applies and all players affected, see above.
3. While not specifically called out, it's a cash transfer. Though, typically those sorts of arrangements do not save a dying airline thus you won't see them frequently.
4. Spirit of rules and human judgement applies here, see above.
5. Buy/leaseback transactions are permitted, within bounds of minimum/maximum aircraft sale values.
6. Spirit of rules applies here as well, it's a transaction to move cash to another airline....
first of all: your are joking, right? i do understand a spirit of christmas (ho-ho-ho), but a "spirit of the rules" is rather ha-ha-ha.

human judgement is a nice thing, certainly, but in the end its about rules that are not creating more doubts than giving answers, and since law should at least in theory bring the same justice to everyone (except you live in sudan or somewhere), there should be a certain precision about them. thats whats called "legal certainty". else i could interpret a "spirit" differently than someone else.
second of all: is there any authority you have regarding the application of rules? i am not a long-time player, so no clue if you are a game admin or just somebody who assumes to interpret the rules at will - because i can do that on my own within the rules set at the manual and we can find very different judgements. would be nice if any known admin could answer these questions; since sami is in the discussion, i would like this clarified by him.
point three: having an answer that contains a "well" and ends with "...." as the last line in your attempt to answer questions really makes the impression that 1) rules are made up on the go and 2) interpreted at will.
basically all you listed is what is called an "elastic-clause" or "ambiguous clause" in jurisprudence - if a jurisdiction is not able to define specific rules within the general set of rules, justice accepts people to interpret them their own way within the interpretability of the existing laws (which would be exactly what you did before if you do not have the authority to set rules - see the second point, or leaving a lot of legal uncertainty - see the first point).
But isn't that the point? If you run your airline like a rational business person, then this unprecise rule will never impact you. It's only when you begin to do irrational things (transferring money to other airlines instead of keeping it for yourself) that it becomes a problem....
a rational business person could say: i invest in an airline in a different country so that i can use profits from that airline later on. for example by reducing competition on the routes between that country and my country. or by getting favourable deals with that company later on. in the end, i would rather interpret it as an investment, not as a gift.