There is a tiny issue which makes the two questions slightly different. But that tiny issue does not mean that each of your suggestions would be a valid question, too.
The Question ‘http://travel.stackexchange.com/questions/30569/do-i-need-a-visa-to-transit-or-layover-in-the-schengen-areaDo I need a visa to transit (or layover) in the Schengen area?’ is rather short and sweet.
I found many related questions on this site but I am still not sure about the rules. How can I decide if I need a visa to transit?
From the way both the title and the question are worded, it seems very much okay to ask (and answer) this based on:
Do I need a transit visa if my itinerary is DME–CDG–JFK?
I.e. that it concerns cases where you arrive and leave the Schengen area via a single airport. This is the usual way that transit (or layover) is understood as far as I know.
The question you are referring to is slightly different in that a change of airports is required. The initerary could have been DME–ORY–CDG–JFK.
As was commented and answered, you have to use ground transport to get from one to the other. That, in my eyes, makes it sufficiently different from a simple transit/layover question which is what the other seems to be asking. Thus, a question of that kind should serve as a different canonical dupe target — however, it can serve as a dupe target for all such itineraries, whether it is LHR to LGW, TXL to SXF, BWI to IAD, NRT to HND or any other combination of two physically different airports.
To be honest, I’m not sure if there shouldn’t be a third canonical dupe for questions concerning itineraries such as DME–FRA–CDG–JFK. These may be seen as two transits in the Schengen area by non-Schengen laymen, while it is actually very much like the ORY–CDG question (except that there are planes from one airport to the other).
However, this answer is based on the current situation. Instead of having a number of different canonical dupes, we can also edit our canonical dupe to explicitly cover all cases. IMHO, that should actually be the preferred path to take.