I believe it's just a different story for big companies. If you heard that Apple was creating "iShoes," you wouldn't be surprised that people were already making branded "iShoes Laces." If, however, I told you I was about to revolutionize the shoe industry, you would ask me how and be generally helpful in the discussion.
I guess the argument would be that big companies already have people with extensive domain knowledge who are deep in the maze, and can afford to be stealthy because they already have 1. History, 3. Theories, and 4. Direct Experience.
The other part is big companies are likely pursuing sustaining or incremental improvements that are perhaps perceived as key to beating out well known incumbents. Startups are likely (read hopefully) pursuing disruptive improvements and might expect incumbents to make classic Innovator's Dilemma errors in assessing risk.
I heard CDixon on PandoMonthly say his key founder questions would surround 'what's your secret?' I think his post provides more context to that line of questioning.
Any evidence for that? We don't get to see the counterfactual of Apple being far more public about what they are building. And we have no idea whether their focus on secrecy is causation or correlation to their success.
Any evidence for that? Stealth mode seems to work pretty well in big companies