A pretty bogus article. If you can charge for an API and people are paying for it, why would you not charge for it? If people aren't paying then think about making it free and making it a doorway into your general product.
I don't think they were arguing not to charge, I think they were arguing a) not to charge an obscene amount, and b) not to charge individually for every little thing someone might like to do (e.g. have a couple tiers but not full-blown a la carte pricing).
I think that if your product is something which is available (by browsing, for example), but you only offer a very expensive API - no stripped down free use - you're setting yourself up to both web scrapers, and giving away potential customers to the competition.
