Four or five years ago, a single mentality dominated the world of web startups: build a service, amass as many users as you could and then – and only then – either figure out a way to make money, or simply get acquired. Then 2009 happened: the economy tanked, the advertising biz took a nosedive and nobody was quite sure what to do. Venture capital funds dried up, and startups that had coasted on business plans that amounted to “eventually,we’ll work something out” suddenly ran out of money. Part of the reason for this was a desire on the part of many Web 2.0 services to remain ad-free. It’s not that they…