Are there a lot of projects that use Git without a hosting intermediary because of genuine advantages? Yes, absolutely. Plenty of core infrastructure and applications, many of which significantly predate Git or GitHub.
Is there a growing subculture of people who essentially equate Git with GitHub and end up completely subverting the "D" in DVCS, incurring unnecessary downtime and who pretend Git/GitHub are the be-all-end-all? Also yes, with circles such as those of HN being overrepresented with "GitHub is your resume" rhetoric and various startups or hip SaaS having GitHub be their single point of failure.
Being the #1 software hosting site in the world does have an effect on demographics, at the end of the day. By now Git and GitHub have an essential, if controversial relationship.