No one is saying that they're invulnerable to defeat at Russian Nationals. Whether or not they earn the spots is dependent on how they skate. I personally feel that Sotnikova has a good chance; Tuktamysheva, slightly less so.
You've said this all before, on several other threads. Top 10 in the world is generally considered a big accomplishment, especially with the strength of this year's field. You're making it sound like they got into the top ten by the skin of their teeth, when, in actuality, the two Russians were WELL in the top ten (by over 9 points).
Their performances weren't nearly as apocalyptic as you describe. Tukt had a freak fall in the SP that rattled her and caused her to pop the 2A. She was actually clean in the FS, landing six triples. Sotnikova had a UR'd jump in the SP that was the result of a season-long problem, and had trouble with her spins like several other ladies. Her FS was weaker, and again plagued by many of the same issues that she's had all season, but was still 9th of the night, which--considering how Kim, Asada, Kostner, Gold, Wagner, Murakami, and Li skated--wasn't exactly an embarrassment.
A "gigantic failure" would be Czisny at 2012 Worlds. Not two upstarts who placed in the top 10 at their first Worlds.