How important are poster sessions in conferences?

Many times I've attended and will attend international conferences presenting a poster in my life. I used to think that this poster works have been considered less important than scientific papers or oral communications, but important anyway for scientific divulgation.

So, when presenting a poster, I've always been thinking: "Okay, it's not as important as a oral communication, but, if they accepted it, this means they found it interesting".

Then I read the "Ten Simple Rules for a Good Poster Presentation" article by Thomas C. Erren and Philip E. Bourne, and I was pretty disappointed after reading point 4:

Rule 4: Poster Acceptance Means Nothing

Do not take the acceptance of a poster as an endorsement of your work. Conferences need attendees to be financially viable. Many attendees who are there on grants cannot justify attending a conference unless they present. There are a small number of speaking slots compared with attendees. How to solve the dilemma? Enter posters; this way everyone can present. In other words, your poster has not been endorsed, just accepted. To get endorsement from your peers, do good science and present it well on the poster.

Do you agree with this statement?

What is the overall importance of a poster session during an international conference?

Is is just a way to collect subscriptions and money, or is it an important occasion for science divulgation?

Thanks

Edit: I'm speaking about poster session vs. oral session, I do know that a poster with presence is better than nothing. As Woody Allen once said: "The 80% of success is just showing up" ;-)