The CEO should not be presenting the app in the first place. Product demos should be done by someone who knows the product inside and out, knows where the unfinished bits are (if any), and has experience presenting products to investors/buyers.
If your CEO can’t ‘sell’ the product / app/ company to an investor effectively, you won’t last.
The CEO should absolutely have the skills, knowledge and energy to sell whatever it is your business does
But, I guess Apple probably has people with better salesmanship skills in each product team than the startup had below the CEO. I'm arguing with myself.
Take a look at the presentation of the original iPhone. It was presented (if I remember correctly) by Steve Jobs himself. But he knew exactly which buttons to press in which order, because otherwise the phone would crash.
I think such an important presentation may/must be done by the CEO, but he must exaclty know that to do and he must prepare very well.