Are these numbers just numbers chosen for the purpose of telling web apps apart? i.e. does the choosing of these port numbers follow some sort of protocol or is it simply just to distinguish between sharepoint web apps for the IIS? I know the default is 80 - but will a web app on 80 behave any differently to a new web app that I create on port 12345, for example? Thanks.
This is more a comment than an answer, but I don't have comment privileges yet. 443, by default, but not necessarily, is for the https protocol. You could use port 443 for another purpose, or you could put your https on a different port. A port is a port, but there are conventions, expectations, and reservations.