[crazygringo]

Even a 10% can rightly be considered a "plummet" in many business contexts.

If a stock drops 10% in a day, that's gigantic. Considering how precarious the profitability of news organizations can be to begin with, a 10% drop that can't be reversed could be the difference between staying in business and folding, depending on how costs are structured.

If your traffic decreases by, say 10%, that's huge -- that's a plummet. (If your traffic decreases by 80%, you don't need adjectives anymore -- you're probably out of business now.)