@Odaly, it is harder for new turkish units to get to new supply centers, and if a retreat is forced on the front line where none is possible, the destruction of one of those units could make the difference between a draw and a solo...
Looking at the first example. I think england on 7 (den, swe, nor, stp, +england) can hold off the entire Austro-Turkish alliance single handed - one unit in den, two to hold stp, and four to hold MAO. No Austro/Turkish fleets in the northern seas makes this pretty hard, so to solo Austria or Turkey needs to stab the other.
(though i acknowledge that a fleet crawling along the coast may be able to break out... it is still hard to get to the point where you've taken everything but those 7... this is not a viable winning alliance, it is a viable vehicle towards a stab of one by the other for a solo.