I recall a Slutskaya interview just before Torino where she said she wasn't going to do a 3/3 in her FS. She hoped the judges would continue to prop up her PCS scores so that sh wouldn't need to do the 3/3. Arakawa may have either read the interview or heard about it from Tarasova.
Sasha was the leader after the SP and had been Irina's main competition (aside from Asada) since Irina's return to competition. Once Sasha blew her FS, Shizuka correctly gambled that Irina wouldn't feel any need to add a 3/3.
Actually Shizuka's coach , Morosov, knew Irina wasn't going to do a 3-3 combo which is why he advised her not to do one. A clean program from Arakawa, and with Arakawa having a huge advantage in the presentation department (both spins and spirals), would put huge pressure from Irina to hit. Honestly, I don't really get Irina. Her advantage is those jumps and she knocked out those 3-3s so easily at Worlds 2005. I don't understand who is advising her to play it safe and do 3-2s. She doesn't have the presentation to beat Shiz (or Sasha for that matter).