My decking was installed with a somewhat uncommon drill bit that isn’t in many people’s household toolkits. Is my decking user hostile?

If there is a valid mechanical/electrical/physical reason why they would choose one fixing over the other, then fair enough - sometimes the more esoteric product can be the correct or only one for the job. If they're just doing it for the sake of making it harder to work with, then, by definition, it's user hostile.

What screw head did they use?

Square. You won’t find square bits in any supermarket or gas station store. But they’re readily available in hardware stores.

Similarly, the screwdriver bits needed to open a MacBook are readily available from computer repair parts stores.

Seems perfectly analogous to me.

Those are Robertson-bit screws, and are ubiquitous here in Canada. (Also a Canadian invention, don'tcha know.) https://www.robertsonscrew.com/

They work great with a power driver, such as you'd want for putting in a deck or fence, so 2-3" deck screws are like my version of duct tape around the house.

It’s just a small star shaped screw IIRC but nothing specific to Apple; other small electronics use these too.