The point of the directive is not anything to do with chronological progression, but to educate people so they stop coming up with silly ideas like, "Michael could give out jobs in Online!" when Michael is retired at that point, something you learn by playing single player.
Its the same retarded mentality that suggests starting Starwars from Phantom Menace, to a new viewer...
Alot of "things" said and done online wouldn't make sense if you played it first
instead of Sp.