Actually no, they usually don't change stats.
And I have been playing this army for almost 15 years. I think I am perfectly capable of seeing a nerf when it happens to them, playing games with the new rules or not.
Besides: no new units and (apparently) no new models means how many people are going to pick up Sisters as a new army that is still all metal, or worse, Finecrap? It's already hard to get people to buy all metal armies. Now you just insured no one probably will. If you think Sisters/WH armies were scarce before, they'll be downright extinct if even existing players don't feel like they are worth playing.
Cheers, Gary