I don't think I've ever been the player on an island, but I have seen it many times.
Concerning groups that ignore the balance and advantage that having one of every class present grants, I have to admit that I will often point out such issues, but only once. Then, I make it clear that I will not alter the world to suit their party make up. I may even give examples such as, 'You will not have anyone to heal your characters, since you do not have a Cleric. Understand, that I will not add hundreds of Extra Healing potions or a Cleric NPC, just because you ignored the precautionary step of having a Priest on hand.' If they don't take steps to rectify the situation (like visit a temple and carefully recruit an NPC Priest or have someone play a Cleric), then they will certainly be tested as players and will hopefully learn from the experience.
I'm not saying I will try and mess them up (people should be able to play the accepted PC classes they want to), but I won't alter the world to make it easier for them. Sometimes the players are up to the challenge of playing a party with no Mages or with only Mages (or whatever) and in those cases, I applaud them, but most often they are quickly undone by their lack of party balance. Hopefully, when this happens, it is not too late for them to correct the situation within the game.
A game I am preparing to start in January has just such an issue. The party has no Cleric. They are fortunate enough to have a lot of Healing Potions from the previous campaign, but those won't last that long and won't make up for the other spells and abilities a Cleric would give them. I curious to see what happens (especially since once they get going in the game, they will not have contact with any other friendlies for a long time).