There is a potential upside to Obama deferring to the Saudi king. By giving the impression, real or imagined, that the Saudi's have dominance over the U.S., it may cause other mid-east states to fall in behind the Saudis creating a sort of "Saudi Bloc". While the Saudis are just as repressive and brutally misogyinistic as the next fundamentalist regime, they are at least nominally friendly to the U.S. This is a stronger and safer alternative to allowing a coalition of fundamentalist states to form around Syria or Iran.
In geopolitical terms, it's not a bad idea to cede local hegemony of Iraq, Egypt, Syria, Pakistan, Lebanon, etc to the Saudis to counter the influence of the Russia, Iran, Cuba, Venezuela alliance that has been developing. I don't think this is what Obama's advisers had in mind, but it could play out in the U.S.'s favor.
Look at me, defending Obama. Because even the silly or wrong things a leader does can be made into a positive.