My impression of The Governor and why he killed those soliders is simply because they may of had items and supplies that they need or could use in Woodbury. I'm sure he'd kill anybody if it looks like they are well-stocked with supplies or have weapons and vehicles. But if there happened to be like an older married couple struggling by themselves to stay alive and away from the walkers or a young woman in her late-teens/early 20s also struggling to stay alive that The Governor would help them, provide whatever supplies they need, and then and let them into Woodbury.... although I'm not quite sure about that because at the end of the episode it showed the head of the helicopter pilot that his team rescued, even though it seemed like he was badly injured he still had a chance to survive with the right care but maybe The Governor decided to kill him because it would of taken too many important supplies like medicine and such to keep him alive. So yeah, I'm not quite 100% sure what factor determines if somebody lives or dies when it comes to The Governor but one thing that is obvious, if it's a small group of people who have lots of supplies, vehicles, and some weapons... then he will have them killed for those supplies.
Now I can't wait for The Governor's confrontation with Rick's group. It's not like they have lots of weapons or supplies that he'd kill for unless The Governor is interested in taking over the prison then I'm sure he'd try and kill Rick's group but they'd be defending what they fought so hard for.
Anyways, this season of The Walking Dead with Rick's group at the prison and Andrea, Michonne, Merle and The Governor at Woodbury plus the possible reunion between Merle and Daryl and confrontation between Merle and Rick has me
for each new episode.