The odds on the alligators showing up in this particular swamp were always going to be higher. The endless posts on pprune about Ryanair and spanish air traffic control demonstrate there is no smoke without fire. No individual component can be singled out as being to blame but the combination was nearly incendiary.
The authorities say getting below minimum reserve or thinking you will is a big deal. Military pilots are of course used to much greater risks. The point is that Ryanair is not the military and its passengers have a right to expect they will not routinely be involved in an emergency situation.
This is a system problem, which hopefully all parties will learn from. The fuel coaches (as some airlines call their experts) will hopefully focus more attention on what to do in the case of diversions with widespread bad weather. Diversions are fortuately rare occurences for most airline pilots. More emphasis encouraging people that diverting with more than minimum fuel in this kind of situation would be a good start.