Shouldn't this thread be titled a "ripa-off?"
Seriously, though - Kristin Chenowith is a star of musicals, primarily on the Broadway stage, though she's also done some film and TV work - she's gained her fame in a totally different way than Kelly Ripa, and I don't really see any valid comparison.
When a male star of stage, screen or TV fills in for Regis, do you consider him a Regis-ripoff?
Obviously, there is sexism at work here. ;D