I mean it's true that any smart player won't walk face-first into Olaf or gank with their buffs up against Nunu, but even that counts as pressure.
Any smart player won't walk up past minions against Nidalee or Zoe = you're forced to sit behind minions and can't play as aggressively.
Any smart player won't play forward when shaco or Evelynn is on the map = shaco and Eve force you to sit back and play at a disadvantage even when they aren't ganking you.
Any smart player will avoid 1v1s with Olaf = it's harder to punish Olaf for playing aggressively unless your lanes already have an advantage, if your lanes are behind or pushed in you have to let him do whatever he wants including taking your camps and pushing you out of your own jungle or risk dying to him.
Any smart player will collapse on Nunu invades = Nunu forces mid to push up and play forward (or risk being unable to collapse when he invades) and risk being ganked, and when he's on the map you can't gank until you've taken all the camps you need. He also pressures dragon and Baron unusually hard.
Even if you don't let them do their thing, they're exerting meaningful pressure