They are still too expensive by limiting you on the number of private repositories and not on storage or something else (requests, etc).

If you are a small business or a freelancer you have a lot of small projects each into a separate repository. So with each new customer you use up another private repository until you have to upgrade to the next plan.

I won't use GitHub until it's either metered (like Amazon EC2/S3) or until they only charge for "active" repositories -- meaning repositories where I had commits or some other form of activity during the billable month.