If that ‘revenue is not relevant’ logic holds true, then it follows that the $99/year annual fee is not relevant to why developers are not releasing extensions.

If that ‘revenue is not relevant’ logic holds true, then it follows that the $99/year annual fee is not relevant to why developers are not releasing extensions. Which negates the most popular (and unsupported) argument against Apple’s model. But if it’s not that fee, then what is it that keeps people from releasing extensions for Safari?