The Head of State doesn't pop off, and it's his business to comment on anything as weird and broken as Ferguson, since it's happening in his country. The racial divide existed, that's why these things deserved to be commented on. The justice system was being used to oppress people so a justice dept inquiry was needed. It seems like a bizarre expectation for the president, who swore to uphold the constitution, to just chill about domestic tyranny.
To me, it seems like your blaming Obama for saying anything but, "Nothing to see here, racism doesn't exist." Which would be cowardly. Now certainly abuse of police powers happen to others (particularly Native American) but racist two tiered policing, and extortion, abuse, and execution of blacks by police are so common place we can't expect any leader to pretend it isn't real.
Now I do agree with the Trayvon Martin verdict to a degree (I think self defense was technically satisfied), but I also understand the outrage of some doofus with no authority whatsoever, stalking a kid with a gun so he could play at being action man.
Should the president give a shit about more white people gunned down for dumb reasons? Probably but white people don't really care either.