On a road car, I agree.
On a car that is driven hard, the diff oil can get hot and deteriorate quicker (same for engine oil).
1. Why I don't strictly follow OEM intervals
According to the maintenance interval for my BP, I should never change the following fluids :
- Automatic Transmission Fluid
- Front and rear diff oil
- Steering fluid
And THAT is nonsensical according to me. To give just one example, we all know that the steering fluid tend to leak on BP's, changing the fluid before it leaks is a good and cheap preventative maintenance.
2. Why I recommend a short maintenance interval
Now, regarding @Conducks 's car, the maintenance interval is the following :
(source: http://www.cars101.com/subaru/maintenance-2017.html)
You probably notice that the Differential Fluid has to be Inspected but never Replaced. But there is a note *3 that states "under severe driving replace every 15,000 miles or 15 months whichever comes first". Based on @1randomkiwi 's comment "All those launches and helis sure take their toll.", I think that we are talking about severe driving here.
Also, I personally think that the engineers that worked on the maintenance interval wrote this note for a good reason
3. Why I recommend a shorter interval than 15,000 miles (=24,000 km) for diff fluid
In racing it is very common to change fluids very frequently, like changing engine oil before/after each race for example. My experience have proven that a car can go a long way with good maintenance (your mileage may vary). I have a couple mates that track cars with 200,000+km and the cars run perfectly, I don't think they would be able to do that without very frequent maintenance like they do.
Considering @Conducks launches his car very frequently and his rear diff is already dying, changing the fluid every 15,000km doesn't seem overkill to me. Even though unrelated to maintenance, what @Kiwi_Fozze said is also to consider in my opinion.
4. End note
I might over-maintain my cars but I am personally convinced that maintenance intervals should be shortened when you drive the car hard.
That being said, you seem like a very knowledgeable person and I have the feeling that your opinion is not so different than mine.
Sorry for the long post, I tried to structure it to make it easier to read though.