Tim Marman points out that the customer is in control:

My "relationship" with Engadget really illustrates this well.  I used to read Gizmodo but switched over when Engadget first offered full-text feeds. Gizmodo has since added full-text feeds, but it was too late: at this point I consider myself a loyal Engadget reader.  It's one of the few sites I will read when I don't have my aggregator.  Even when I do, I still visit the site a lot to leave comments.  I also link to them a lot, and while I may not have Scoble's 18,000 readers, I send some traffic your way - that should at least help make up for the "lost" visits from me, right? ( Oh, and unlike Robert, it's not that I actively refuse to link to sites with partial-text feeds - it's just hard to link when I've already unsubscribed and won't see your content ).

It's really very simple: RSS lets the customer control the conversation.  In exchange for that control, we will gladly reward you with our loyalty - and we'll be happy doing it. But if you're going to do this, you can't do it half-assed - don't give us partial feeds!

I'm not as hardline on partial content as Tim or Scoble are, but that's not the point - the point is, customers have a lot more power in the conversation than they used to. Marketing departments are figuring this out very, very slowly.