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].
***
Now, 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.

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

For big planes, there seems to be, Ryanair has a fleet tailor-made to have a MTOW of 66,990 kg (WF ~36.60) for similar reasons [apparently][3], or they're just being cheeky.


  [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