It's nothing more than playing catch up.

I'm company X and I 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.

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 [matches that weight][1].
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There's something called [Weight Factor][2]. It's **SQRT(MTOW/50),** MTOW in kg.

The Weight Factor is used in calculating the charges the operator/owner pays for taking off, landing, transiting, parking, etc.

*That's why it's vital for competitors to have similar MTOW's.* To market similar operating costs.

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][3], or they're just being cheeky.

It's also why some airlines don't choose the Extended Range. The 777-200 and the ER version are the same apart from extra certification and a **higher official MTOW**. But they can request conversion to ER later on if they open routes to farther destinations.


  [1]: https://en.wikipedia.org/wiki/List_of_airliners_by_maximum_takeoff_weight
  [2]: http://www.eurocontrol.int/articles/establishing-route-charges
  [3]: http://www.pprune.org/tech-log/494333-ryanair-mtow-66990-how.html