Helping Webber celebrate were figures like Ross Brawn, Jenson Button, Lewis Hamilton and even Sir Frank Williams, who was carried up the 16 stairs in his wheelchair.
"We are no longer friends, but we respect each other," Vettel is quoted as saying.
1997 world champion Jacques Villeneuve, meanwhile, backed Red Bull's decision to replace the Le Mans-bound Webber with in-house talent Daniel Ricciardo.
"Vettel has developed so much this year -- he's super fast but he no longer makes mistakes or freaks out. He's made the biggest step of his career," said the French-Canadian at Monza, who has previously been critical of Vettel.
"So why would they have signed a driver who disturbs the peace? Daniel will be easier to handle politically than Webber," Villeneuve is quoted by Auto Motor und Sport.
"Does he have broad enough shoulders to withstand the pressure? We will not know until next year. We'll see if he's still grinning then.
"But I think it's good Red Bull have taken a driver from their own school -- other teams also encourage young drivers but really all they do is talk about it," he added.