Maybe JP & JPJ didn't attend Robert's son's funeral because it would have been a fiasco, in that there world have been crowds of people and in doing so create a circus atmosphere. One can only speculate, I think that with Page's dabbling in the Aleister Crowly shit may have given the press a field day.
I never thought that ITTOD was anything more than a Robert Plant solo record, I think Zep stalled after Physical Graffiti, maybe the double disc was an out as it could have been a single lp; Presence could have had the overflow and been a much better record.
At any rate after Presence it was clear Zep needed a break, it couldn't have gone on much longer anyway. They did so much in a short period of time, just like The Beatles did, you just can't go on after that kind of 'rocket to the moon" succsess, you give 110%, it can't last. If either band had stayed together they would not have the legacy they have today. You have to leave people wanting more. The Stones have gone on way to long, same with The Who, they changed music but you forget that because of all the crap recordings since.