Peer review isn't the same thing as validity either. Both are proxies, sales are simply a much better proxy. Especially long term sales from an established company.
Look at it like this: a Peer Reviewed (tm) article comes out saying "Foos cannot Bar, it is impossible". The same day, Apple releases "Bar for Foos, $8/month". Over the next year you see media outlets discussing how well Foo Barring works. Online reviewers talk about how they've incorporated Barring their Foos into everyday life and it has benefitted them in all these great ways. Your colleagues at work mention their fruitful Foo Barring adventure over the past weekend. Routine posts on HN come up where hackers describe how they've incorporated the Foo Barring API's into their own products in some novel way.
Your mother then calls you up to ask if she should get involved with this new Foo Barring thing. What do you say, can Foos Bar?
