If the only precautions the orcs take is to cluster tightly around a single bonfire, they deserve to suffer the effects of Darwinism, as applied by adventurers -- Something the article makes clear.
What the article doesn't make clear is this:
1. DMs learn from their players. A DM who doesn't learn from players' actions and plans is shorting himself. Go ahead and give the PCs their easy victory. Then come up with a few basic counters to make it more interesting next time.
2. Things aren't what they seem. Your players may be smarter than you, they may be more tactically talented than you, but they will never know as much about the encounter as you. Just think of the potential havoc if there'd been a single Doppleganger in among the orcs. Or an Outsider. Or an earth elemental, summoned by the witch doctor, hiding in the ground and helping keep watch. Or maybe an invisible stalker or three along as escort for said witch doctor.
3. Word of tactics and strategies gets around, or has already been thought of before by in-game creatures who are far smarter than the DM, the players, and the PCs all put together. Justification without metagaming: In general, if a PC comes up with a great tactic, the god-like intelligent, long-lived, movers-and-shakers of the campaign have probably thought of it or similar tactics also, and will train their troops. Or the PCs pass the tale onto bards, for free food & drinks, who immortalize the PCs exploits in song and tales... and incidentally, inform all the other orc tribes how not to be chumps.
4. Explore a little military strategy research for fun & challenges.
5. Read message boards, talk with other DMs and players, expand your horizons. I've lost track of the number of ideas inspired by, or taken directly from, other sources.
6. If nothing else, follow through with the logical consequences. What if the remaining orcs scatter out into the wilderness in groups of 5-10? Now the PCs have somewhere around 100+ orcs, scattered but not so far away that they can't signal each other, at night, in the wilderness. Good-bye rest & replenish spells/powers time; hello commando-style survival (mitigated greatly if someone has rope trick or a similar spell).