It's entirely down to a sense of entitlement. Be it a real sense, or an imaginary one. Ultimately it doesn't matter since the effect is the same. I wrote a blog post about this exact subject a while back since it constantly irks me when I hear people say "oh, my favorite internet service just started charging me a buck to use it, time to change".
I'm not entirely sure what the policy on linking to ones own sites is on this forum, hopefully I'm not crossing a rule here. My blog is entirely harmless after all, the worst thing you'll see are pictures of my cats. In the off chance that I -am- violating a rule, then I ask a moderator to slap my post with the moderation hammer. Here's the post in any event,
http://anders.tonfeldt.se/?p=790
Unfortunately this entire topic is a dead badger, it doesn't matter how much we poke it, the darn thing will still just lay there. It's impossible for a producer (of any type) to change the behavior, or indeed attitude, of consumers at large. You can reach out and change the mind of individuals, but that won't get you far. If one doesn't adapt one will eventually die out. I'm not saying this in some kind of prophetic "doom is upon us" fashion, especially since the concept of "free" isn't actually -free- anymore with the advent of freemium. I've made a lot more money with my free products than my paid for products, there, that's a better way of putting it.