The issue for partners in many instances is 'the last mile'.

For example, United, Delta, Northwest,American, Continental can get pax to key gateways in Asia, Europe and South America; their alliance partners are responsible for the domestic or regional segments, which typically don't have the limited availability like partner international segments.

Clearly, airlines like Alaska, Midwest, Frontier are much more dependent on intl. partners since they lack such service. Those airlines are in a far more precarious situation in delivering on their promises for intl. destinations.