2. You probably notice macs more because of their uniform branding, compared to a mish-mash of different looking other laptops.
3. Is it not enough to watch and listen to a keynote without pulling out a laptop?
4a. Dual booted, is it running macOS, Linux, Windows, *BSD?
4b. Is it running a VM (or more than one)?
4c. Is it used as a very expensive terminal with SSH to a different *nix OS or a remote desktop system?
At various times, all those have been true of mine.
Strongly recommend reading this response by Terry Lambert on getting OSX to POSIX compliance.
https://www.quora.com/What-goes-into-making-an-OS-to-be-Unix...
The prevalence of MacBooks at tech conferences is in my experience a very US-centric thing. I rather associate ThinkPads with tech conferences.