The difference here is that it's not marketing intended to deceive and make money, it's just happy consumers that want to help the project and make it known.

Corporate marketing people though are paid to abuse psychological vulnerabilities of the target audience, over-exaggerate the pros of the software and hide the weaknesses under the carpet. I'm not saying that it's an inherently evil job or that they're not needed in a business, I'm just saying that as a developer I'm tired of software being a product and a business, when I simply want to create good software that solves some kind of problem and not be a cog in some corporate machine.