This is so incorrect that it's hard to take seriously.

When revenues go down (for any reason), companies cut costs. Most employees are a cost. Why have 2 people when 1 will just have to work harder? A company rather cut and see what happens, when push comes to shove. Many company initiatives are also re-evaluated with a bottom-line mentality when revenues are down. That project that's 4 weeks overdue for a milestone? Time to cut it and everyone involved. When revenue is up, the opposite effect. "slack" is relative to market conditions. Job security along with it.

Small companies are often lean, but it's never surprising how much leaner they will run when money gets tight. Big companies can always pare down assets and associated headcount. These are just the things I see every time revenue is down, but far from an exhaustive list.