My point is that the situations were different. you mentioned the last four Kings captains were traded, so by that I assume you mean Rob Blake, Matthais Norstrom, Rob Blake again (was captain both before and after Nortsrom) and Wayne Gretzky.
Gretzky was traded as a UFA to be who was 35 and wasn't going to resign in LA. LA as well had mised the playoffs the previous two seasons and would miss they again the year Gretzky was traded, as well as the year after. We were in a rebuild.
Blake, essentially the same thing, though a contract dispute was added. He was a UFA to be, we were a team which, at that point, wasn't even in the playoff picture. He was dealt for future assets.
Norstrom, again, same thing, though I think Norstrom had one more year left on his deal. We however were set to finish with the 4th worst record and were just starting the rebuild under DL.
The second time Blake left as captain, he wasn't traded. He left as a UFA and signed in San Jose.
Point is, different set of circumstances. Brown if he was a UFA to be, or nearing the end of his career, on a team that is rebuilding or in the dark times, yeah, he'd be gone. Same as many other captains on other teams. Iginla, Morrow, etc.