Hi,
we do not know the real reason yet, but I am personally really affraid, that this might be a legal issue and that Suchoj asked OM to remove Su26.
Su26 family of aircraft is still in production and I can imagine Olegs virtual model of this type being so perfect (do you remember Luthier metioning for example that the COD engines simulation is simulation within simulation?), that someone at Suchoj company might consider that there is a lot of sensitive data inside, being released to public (well encoded, but still ...).
I hope that this is only construction of my vivid imagination and that I am completely, utterly wrong..

.
O.