Why can't a copyright be more like a patent -- or vice versa?

The IPKat's friend Hugh Wright (Brookes Batchellor LLP) has been stirred by the recent publicity next month's Copyright Debate into posing a question which this member of the Kat team is refraining from answering from a purely historical perspective, since it has been posed in terms of contemporary utility, not legal evolution.  He writes:

"I have never understood the true difference between the reason for patents and copyright (I know that copyright is only infringed by copying and patents can be infringed without copying - a difference without meaning in practice).  It seems that the same principles should apply to both, at least so far as commercial exploitation of copyright is concerned. They are both the work of someone's imagination and brainpower. They wouldn't exist without that.

So why shouldn't patents extend for the lifetime of the inventor plus a number of years?

Or why shouldn't copyright require registering (easy, no examination required) and the payment of annual fees and last for 20 years?

The Treasury would love both those suggestions!"

The Kat has, over the years, spent considerable time (and derived even more pleasure) from speculating on such issues as 'why can't dogs be more like cats?', 'why do holders of domestic passports and foreigners have to go through different channels at the airport when they don't get sent back if they've got into the wrong line?' and 'what's the difference between fruit juice and fruit drink?' But he has always been quietly confident that he knows the reasons for the differences between patents and copyrights.  For this reason he has decided to invite readers to offer their own explanations. What do you think?