You state this confidently but I don't see why it's true a priori. I don't see a strong correlation between Apple's cash on hand, assets or market cap and the severity of a zero day in Mail.app.

The better comparison is active users, weighted according to how many apply automatic updates. The vulnerability half-life probably isn't as devastating as you might think it is since Apple has centralized control to push out updates, limited only by users deliberately not installing them.

I would consider a vulnerability in OpenSSH to be far more economically devastating, and there isn't even a company with a market cap behind that software.