As previously reported, John Cena was at RAW on Monday, but was only used in the dark match segment that night. The Rock had a previous commitment to be overseas in South Korea promoting G.I. Joe: Retaliation, which is why he was not there.
WWE officials made the call to keep Cena off of the show because they felt that Cena appearing on camera would have been a reminder that The Rock wasn't there. They opted to keep Cena off camera and went with the video package to build the feud that way.
As noted earlier this morning here on the website, There was a lot of talk at RAW this week about current WWE Champion The Rock not being in attendance. Several talents are upset at the fact that he's not going to be at two of the next four RAW broadcasts leading into the WrestleMania 29 pay-per-view. There was already some resentment over him being in the WrestleMania main event and this doesn't help matters any.