I don't think celebrity gossip is considered news because lots of people are stupid. Despite the lofty topics you mention 'serious' papers still inject these stories with conflict and narrative structure. The same things that make celebrity gossip stories. Serious papers don't carry data and reports on issues unless they are 'sexy' (in the UK, the dossier claiming Iraq could deliver WMD in 45 minutes was widely reported to have been 'sexed up').

I think a better question is what role do stories play in society? It's a bigger question than I can answer but I think celebrity gossip may, in some ways, be a substitute for morality tales or quasi-parables. The hedonist party girl gets her commeupance and goes to jail / goes insane. Funny how it's always a girl though...