Or selectively telling your buddies in teh know and helping them to fix their shit, while keeping uncool kids out of the loop. Now that's irresponsible.
And at other times 90 days maybe inadequately short. But 90 is just a round number someone at Google thought is a good idea. And now it's become 'standard'.
I can go with immediate, or I can go with never. But realize that every vuln is different, and their impact (or hardship of writing or applying patches) may not always be fully understood by stakeholders involved before or immediately after the details are released [CVE-2015-0235].