If you watched RAW, you saw that WWE Champion, Alberto Del Rio, didn't appear on the show. The fact that it was a RAW "Super Show" made his absence all the more confusing.
It seems Del Rio went back to Mexico this weekend to renew his work visa. This is not unusual as any non-U.S. citizens must return to their birthplace and to have this documentation up to date.
Del Rio was initially expected to be back and appear for RAW in Tulsa but obviously that didn't happen. As of now, he is expected to be at the live Smackdown on Tuesday.
According to one source, other than Cena making reference to Del Rio in his promo, the WWE didn't make any more mention of Del Rio's absence because they had no explanation in the storyline that would have made sense. WWE wanted to disguise Del Rio not being on RAW with the other storylines going on such as CM Punk/Kevin Nash/Triple H and with the amount of star power the show had featuring talent from both brands.
In addition to not appearing on RAW, Del Rio was not promoted for the Smackdown show during several of the promotional spots as they didn't want to bring up his name and appearance for Smackdown Tuesday without having to explain why he isn't appearing on RAW.