I think this isn't what Seth meant: there's a lot of consultancies turned into product companies but it's different to start running a startup and then to work with your clients to find product market fit etc.
At least one example is http://rjmetrics.com/ - I saw the founder speak for a class I was in a few years ago. Their story is basically that they went to small companies offering analytics services and shaped their services based on what these companies asked for.
