What is the significance of the 10,600 lbs MTOW limit? I recently noticed that several airplanes have MTOWs very near or exactly 10,600 lbs. That was an interesting phenomenon to me because I am familiar with the 12,500 lbs MTOW regulatory limit on certain types of small planes, and familiar with the 19,000 lbs MTOW regulatory limit on certain other "commuter" planes, but I couldn't find anything to support why so many airplanes would have MTOWs at 10,600 lbs.

As I tried to google for "10,600 lbs max takeoff limit" I found more planes that are at or very near that exact MTOW but couldn't find the basis for why this is.

Does it have to do with European regulations? Does it have to do with insurance considerations?

Airplanes with near or exactly 10,600 lbs MTOW


Cessna CitationJet / M2
Beechcraft King Air C90 / and derivatives
Embraer Phenom 100
HondaJet HA-420


EDIT: A Little More Info

I have noticed that 10,600 lbs is very close to 4,800 kg. So its possible that this regulation stems from something non-FAA, something that regulates in kg, but even still, I haven't had any more luck with Google trying to figure out what the derivation of a 4,800 kg limit might be. Yet again, all I found was yet more planes that have that same MTOW limit.
It's nothing more than playing catch up.

If company X managed to build an aircraft for a certain mission at the lowest ever MTOW. Company Y will try to get down to that MTOW to be able to compete. Lowest is good if the mission is the same.

Check the MTOW of the Airbus A320-100 and the Boeing 737-400, to save you time, they are 200 pounds apart. But the A320-100 didn't sell well, the A320-200 did. Guess what, the 737-800 matched that weight.



Here's why:

There's something called Weight Factor.
$$
\text{Weight Factor}=\sqrt{\frac{\text{(MTOW in kg)}}{5}}
$$

The Weight Factor determines the route charges.


  This charge takes into account the distance flown and, less than proportionately, the aircraft weight.


That's why it's vital for competitors to have similar MTOW's. So they can advertise similar operating costs. MTOW is also used in airport fees.

The only interesting thing about 10,600 lb / 4,800 kg is that the weight factor is kept a tad under 10.00 (two decimal places are used). Now, is there a higher charge for a plane with WF at or above 10? I scoured the internet, there doesn't seem to be WF brackets set that way, to my dismay.

Ryanair has part of their fleet tailor-made to an MTOW of 66,990 kg (WF ~36.60) for similar reasons apparently, or they're just being cheeky.

It's also why some airlines don't choose the Extended Range. The 777-200 airframe and its ER version are the same (no auxiliary fuel tanks).

The differences are extra certification for higher MTOW, and the same engines but certified for higher thrust. Airlines can request a conversion to ER if they open routes to farther destinations.