This is a good question because it shows how many different ideas are out there in regards to the "why and what" people consider they are doing.
When looking at karate they will block and counter strike. Jujutsu will use blocks and parry into technique. In Daito Ryu, aiki is basically defined as breaking the uke's balance as soon as contact is made. Most Daito Ryu people think that aikido people take too long to break balance. In aikido we use blending and the leading of uke's energy into a technique as aiki. So I would say that aikido is "not stopping the energy of the attack but letting the energy of the attack turn into technique".
By not stopping the energy of an attack and then taking the balance of uke we are doing aikido. The completion of technique could be a throw or strike but the lead up to the completion is aikido. As has been pointed out other styles have similar techniques but they do not move and break balance the way aikido people do.
Just my thoughts.