Out of lazyness or out of actual usefulness to the users?
A little of column A, a little of column B. Arch is very much a distro developed for the packagers. OTOH, as someone who often has to dive into the details regardless of distro, I generally appreciate the plain-vanilla approach to arch's packaging (since I can just set the package up as opposed to undoing whatever helpful defaults and changes Debian's decided to add).
I personally (using Arch, btw) definitely prefer Arch's behaviour. If I update or install a daemon, I generally want to configure it before (re)starting it.
Restarting it and telling systemd the .service unit has been changed aren't the same thing.
Arch does daemon-reload after service file update: `(2/5) Reloading system manager configuration...`