In some cases i agree that there are mature alternatives, but what if you dont want or cannot use them. For e.g. Dropbox is a great file storage/sync service. But you may not be able to use it inside an enterprise and store office/confidential documents.
I think its essential to know and understand various ways in which a tool can be used. So that you can apply it to solve/simplify a problem. Its not a marketing.
Despite the existence of 'solutions', there are lots of interesting things people can do with git and it's probably fun to explore them.
edit: I'm not sure why you consider it 'marketing' either.
And frankly, is it really different from using someone else's library or module?
No specialized wiki software can be a DVCS or backup system.
The right tool for the job is always the right tool for the job.
Git is not the right tool for the job for most of the cases described.
But imho, right is a subjective word. What is right in one environment is not right in another. The intention of the post is to be aware of the possible uses of git. Its not to say that its best for all purpose/cases.