We chat about videogames and videogame accessories.

(A bunch of very good points)

I can see where you're coming from, but I'm still not quite sold. The white block was a really good example of a secret you can't know about through gamesense alone, but that's exactly where the Sonic Adventure secret and your example differ: You do know that there's something up there. You can see the platform, and you can seen the ladders, and you can at least assume that you'll have to do something to lower and raise that platform to get to the ladder to see what could be up there.

And that's exactly why I think the secret is designed poorly: It makes you /think/ the answer is something intuitive when it isn't. You're left to think you're missing something somewhere back, or can't see a lever with which to work the platform. An analogy would be that the chest with the whistle from level 3 is in plain sight at the level's exit, but won't open unless you ducked through the white platform. The way the level is designed does let you know you're missing out on something, and makes you believe it's your fault, so saying "what you don't know won't hurt you" in that specific case doesn't hold water.