It's not very clear, but if written in our checklists it takes a bit of judgement and common sense as to what a suitable airport is.
On the 777,or any twin, something like an engine requires the aircraft to 'land at the nearest suitable'. For us, in Cathay, this means land at the nearest 'Company' suitable. This is a list of airports that Cathay has assessed in terms of runway length, paving strength, fire services, ATC services, availability of parking bays etc.. On our route network, we are never far from one of these airports. If we have an engine failure or other 'non-serious emergency' (If there's such a thing!) then we can bypass the nearest airport to proceed to one of these company suitable airports. If fact we are even given the choice of bypassing one company suitable airport for another, if the distances are not too different. We may want to do this to divert to an airport that Cathay has regular services to. This means there is passenger and engineering support which in turn means less delay and hassle for the passengers. The Captain may choose to do this if he feels it is in the best interests and safety is not being compromised.
With a fire onboard, like an uncontainable cargo or cabin fire, or even an uncontrollable engine fire, there is the risk that the aircraft may not make it to an airport far away. They say that a large cargo fire only needs 15-18 minutes to burn through the flying controls and cause the aircraft to be lost. In these cases, you need to land on the nearest strip of concrete, or consider ditching. If you are in the middle of the ocean and you have a confirmed and uncontained cargo fire, your only option is to ditch. If you are near land, then land at any airport nearby, large or small, or a road, or anything like that. There will be casualties, but it's that or crash. We are trained to make decisions like this, but hopefully we never have to make them.
Ultimately, safety is everything. The lives of your crew and passengers must override all other decisions and if it means the aircraft will be written off, then so what? We are allowed to throw the rulebook out the window in the name of safety.