The wasps are out in force at the moment as they no longer have brood to look after, and therefore are not only , but also deprived of their sugary hit they have been getting from the larvae. Wasps catch meaty prey for the larvae but cannot digest it themselves, so chew it up for the grubs, and in return receive a sugar-rich exudate from them. This is why they are after our ham sandwiches in early summer, and then jam sandwiches from now. I am really keen to stress that wasps do an amazing job of predating many pest species: this article gives an idea of their importance in the ecosystem and I would encourage all of us to be appreciative of their value.
My apple trees are smothered in starving worker wasps at the moment, and a hive full of honey is an irresistible target. Bees and wasps have coexisted for millennia and I feel the demonisation and destruction of wasp nests is something that will come back to haunt us if it continues. Many beekeepers feel completely justified in destroying wasp nests as soon as they see them; wasps will attack bee colonies and rob the honey. Bear in mind that other bee colonies will attack and rob honey too so it is not just a wasp problem! The best way to prevent trouble from bees or wasps is to ensure the hive is bee tight, so no gaps in the woodwork, and to reduce the size of the hive entrance.
Close any top entrances, and if you have a gabled roof or a WBC, block the conical wasp escapes on the lid with a loose plug of paper. If the entrance block has a choice of apertures, swap it over to the smaller one. Unless it is a new colony, the bees will have propolised the entrance block in to place so sometimes despite a tug with the hive tool, it doesn’t want to come out. In this instance, it’s best to cover part of the entrance with a flat piece of wood, plastic, or even cardboard at a stretch, and tape it in to place. Wooden spatulas or lolly sticks can be used, or improvise with a judiciously wedged bit of stick. If the wasps are really going at them, reduce the space to a centimetre. This can be policed by a single guard bee, and although the returning foragers will have to queue to get in, better this than the hive being robbed.
Mature colonies with a strong queen and established combs kick out a lot of pheromone which will deter wasps and errant bees, as well as the sheer number of guards. Hives can become quite aggressive/defensive at this time, and removing honey or any checks should be done efficiently and as quickly as possible to keep the bees as secure as possible. Carry a tin or lidded tub to put in bits of comb or any arisings from the hive as the scent of broken comb can attract undesirables.
Wayward Bee 
At one point there was a wasp nest living next to my hives – they all survived. As you say strong colonies can cope fine with wasps.
It’s certainly been my experience that wasps only seriously target weak or small colonies, which is an obvious evolutionary tactic!