Weighted voting is different from merely having editors, because there are two steps. The editors don't pick the stories. They (in effect) pick the people, who pick the stories. Sort of like the president picks a Fed chairman,
but does not directly control the money supply.
Sure, but you wind up with the monetary policy that the president wants, not the monetary policy that you would get by democratic vote. (Though perhaps the analogy with the Fed is a little akward because monetary policy is something most policy makers agree on, not a matter of contested opinion.)
With weighted voting, the stories that wind up on YC news will closely reflect the desires of the editors. That's fine, but it's not a democracy. It's more like a benevolent dictatorship! (very benevolent ;)
Of course, in truth I might be quite happy with this system. I've liked what the editors have let through so far (though last few days less so) and I would probably rather read what they suggest than what the "group" suggests.