The differece is commercial use.
Sami gets money from us for AirwaySim, AWS is a commercial project and as this it isn't allowed to used pictures etc. without permission or license. Exceptions from this are some very special things of daily life, like aircraft names (but this is not EU law).
Ilyushin is just a private person who linked this. And this should be ok as long as hotlinking isn't forbidden by the source. In this case it would (German law only) also be ok if he copies the picture and uploads it himself, but clearly with shown watermarks and sources.
Again, US law can be different. I don't know, my study focus is German law with parts of EU law.
PS: If arliners.net is also a commercial website, so these pictures are only available in a special member area one must pay for, it wouldn't also be allowed to be linked here or copied and uploaded. I don't know airliners.net, so I can't make a clear statement on this!