Regarding Alberto Del Rio being pulled, WWE officials looked at the 12-man match and felt that Del Rio didn't fit in it. They are planning on pushing Del Rio soon and didn't want him in a match that will be full of comedy and other shenanigans. With that said, it's interesting to note that they kept guys like Dolph Ziggler, Jack Swagger and The Miz in the match.
Sometimes... a facepalm is not enough...
Orton's a solid worker and the matches will be nice, but as you say, the promos will be unbearable. Hopefully Del Rio practices more lines, and the feud will be a "Hurr, you attacked me in a random irrelevant Smackdown match! I must beat you down for the next four weeks since I'm the unhinged Viper and noone escapes my strike!" You know, like his feud with Kane... And Barrett... And Cody...
How on earth is Orton as over as he is?