Actually, Radionova didn't fall at Worlds in 2015. Over the past 2 seasons, she's only fallen 3 times (both GPFs, like you said, and CoC 2015). That being said, A LOT of her jumps have messy landings. So Radionova is consistent in that she gets the jumps done, but she doesn't
consistently get +GOEs.
Medvedeva, on the other hand, has fallen more frequently, but every other jump gets +GOEs so it almost doesn't matter.
Also, both of them pop jumps very, very infrequently, and popped jumps are far more costly than a fully-rotated jump + fall.
Some tech specialists (tech controllers?) have a reputation for being very strict--Shin Amano, for example.
Which reminds me, when do we find out tho the judging panel and tech panel for Worlds will be?