It is rather costly to be there and Nintendo was there but not all the time. when they are succeeding… they show up to promote. when they are lagging… they still do their own thing to promote.
As for sony, they certainly arent lagging so their reason (as they said) last year was they had nothing to show other than what was shown before. They cant use that excuse this time. They have stuff to show and they would be foolish to skip again. They were one of the principals behind driving E3 to its success… it is bad form for them to back out of this year even though they can still have their own event prior.
If the rumors about their dealings with the ESA were true then people wouldnt get upset if Sony just said, “we dont like dealing with the ESA and have decided to back out of any further E3 shows” but instead… they said we have nothing to show this year which may have had some truth to it but it also sounds like a lie to cover their issues with ESA. They don’t need to protect us, they can be honest and people will understand.