It applies to Google. Their main revenue still comes from Search Engine Advertising, which is a really good customer acquisition channel.

But the reason ad spends decrease during downturns is that people consume less, so there's no point in advertising when nobody's buying.

This is opposite. Marketing budget is second to be cut first being building (space expansion). The R&D budget however goes up mid recession. Here is how the cuts work R&D, space expansion, marketing, parties, raises, new product building, warehouses,