I think the main thing is that new technology routinely builds on top of old technology. Sure, it would be nice to still be collecting royalties for your 100 y

I think the main thing is that new technology routinely builds on top of old technology. Sure, it would be nice to still be collecting royalties for your 100 year old patent, but you can't build anything new unless you license all the technology that came after it. The cross licensing necessary would simply mean corporations having to shovel vast sums of money to legal firms. It's simpler, cheaper and better for corporations to have patents expire. As another poster commented, we are starting to see large software companies realise the massive downsides to software patents and I suspect that we will see those restricted even further in the next 10-15 years. For copyright, on the other hand, certain franchises are worth lots of money but there is a limit to how much you can build on past works. Disney could theoretically insert Mickey Mouse into every film they make, but that grows old fast. They have to create completely new stories, characters, etc to make money. There is very little incentive to cross license most creative works. Even where it is done fairly liberally, for example American comic books, I think you could argue that it isn't necessarily a good idea. Apparently the most lucrative approach seems to be to exploit something while it is popular, then sit on it for 20-30 years before you "reboot" it for the next generation. What the copyright lobby is protecting against is that potential "reboot". They generally don't want it to be used in the meantime. I think this is one of the areas where the FSF gets things right. It's really misleading (and potentially dangerous) to lump "intellectual property" into a single bin. All of the things commonly referred to as IP are really different in terms of motivations of actors and consequences to society. Would anybody seriously argue for time limits on trademarks, for instance? It would be an interesting world if anyone could sell "Kellog's Corn Flakes" just because the trademark was old ;-).