Balesir
Adventurer
The latest specific quote is in the Rules Compendium, pp.212, lines 6-8.The movement doesn't look optional at first glance, but it might be buried in the general rules, I suppose.
If the GM specified, in advance, that this specific location was a bare, 20' square courtyard with no steps, no doorways, no braziers or torch sconces, no barrels or crates or other impedimentia in it whatsoever, this objection might stand. I doubt, however, that this was the case. It was simply a generic "20' square court", and as such it might reasonably have had all manner of detritus, street furniture and other obstacles in it. The GM simply, in effect, chose to make it bare and boring on the fly.Things are what they are in the gameworld. Changing the nature of something on the fly to suit narrative concerns IS a problem with the system. It means engaging in illusionism BS instead of running an honest game.
If he was a L1 brute then the fight was always going to be long. That's the way the world works. If "muggers" are generally L1 brutes* then so be it. If "normal folk" are minions then they probably expect an easy win - so I would imagine they would run away from a real fight. Make him try that and the fighter might get some reasons to push him into a corner...Either the mugger was a L1 brute or he wasn't. Assuming he was, then the system says 10 rounds of combat to take him down isn't uncommon. If you enjoy a long fight with a thug then the system is working as intended. If you don't, then once again there is a system problem.
* As a complete aside, I would think most muggers would be better seen as Skirmishers than Brutes, but whatever.