Shouldn't whistle-blowing be much easier in a more transactional work culture where everyone knows you can't count on the company and they'll fuck you over next Thursday on a whim of some consultant or an ambitious upper manager?

That entirely depends on the current economy. If they know they might have opportunities elsewhere, toot that whistle..

Sadly no. The world is litigious. The expection is that a wealthy corporation will crush anyone who holds it accountable.