Once you get to the question of whether a specific etiquette is required then I think that things get much cloudier.....
I think that if you ask people "should etiquette be required?", then most will say yes. Once you get into the details I think that most will say "no".
I tend to agree, and I think this has to do with the human desire/need/preference for some kind of ritual, however brief, to separate disparate activities.
If I dash into the studio or out to the garden for just a two minute task, I don't bother; however, if I am planning on settling into either for a period of focused work, then there is a period of tidying up, preparing tools, etc that may or may not be 100% "necessary" but helps me prepare. Similarly when doing major cooking or arriving at the office.
I think much of what falls under the rubric of etiquette in the aikido dojo is simply THAT dojo's specific ritual norms that help separate being in the dojo from other activities and therefore aid in focus (as well as, being communal rather than individual, team-building).