I think TSK and CK have nailed it:
TSK: "It is attitude, not latitude".
CK: "Regular cruising is going where you have to bring your own ice.
Expedition cruising is where you bring
equipment to chip the ice and fend it off."
Either or both can apply.
So it's still possible to 'cruise' the high latitudes, as El Pinguin (and others) do, without it becoming an expedition, even though ice may be present. But if a major intent of the
cruise is, for example, 'peak bagging' like Tillman and others since, then that should be classed as a 'mountaineering expedition by sailboat', perhaps.
It's equally possible to do the 'Drake
Passage Dash' and 'cruise' the Antarctic Peninsula, without it being an expedition. Several well-equipped sailboats do this ever 'season'.
In the past, early cruisers such as David Lewis, set themselves up as 'psuedo' or 'minor' scientific *expeditions* in order to get either recognition or some form of
funding to assist them with travel to difficult areas or for 'specific purposes'. Hence, 'expeditions'.
For example, Lewis' travels in
Isbjorn were in the tropics, but were designed to 'test' the then almost extinct 'Poynesian traditional'
navigation methodolgies which, largely as a result of the
books he published as a result of that 'expedition', lead to a revival in Polynesia of their trad skills and teaching these to younger people.
He also sailed
Icebird to Antarctica, and had to leave it there after it was dismasted while he went back home to raise funds to
repair it and continue what was, essentially, an 'adventure' rather than an expedition. But given the degree of difficulty, it still should be called an 'expedition' in my view.
Ditto Ben Tucker's
family trip to Antarctica in
Snow Petrel - the book of the same name by Dad, Jon, (the
cabin 'boy' and 'dish bitch' on the trip) is an excellent read by the way, but it had no clear or defined 'scientific purpose' but was most definitely a test of organisation and endurance. And given the indemnities they had to provide to authorities in order to get 'permission' to sail there, perhaps that's another we should add to the qualifications for an 'expedition' - "authorities require application for permission" to go there.