The law depends on where you live. In the US a physical book can be loaned, given away of sold without limit. It can not be copied but as long as you give away the physical book it is not being copied. Other places may have more restrictive laws
That is partially because you have to give it away if physical. The "loan" is really just an agreement you'll eventually give it back.
If the e-book were transferred, could do the same thing with it. However, that would mean deleting the book from all Kindles connected to that account, invalidating any "back up" they may have copied off the Kindle to the local computer (or somehow rendering that unreadable somehow), transferring the book to the friend and then repeating the process at the end of the loan.
Not sure if Amazon has built a "delete" into the system that tracks your library. There would also be a number of folks freaked out by the "delete from my Kindle" feature. Apple has a kill switch, but they go out of their way to say they don't want to use it either (except under extreme circumstances).
That would be nice if Amazon did that. I'm not sure they have fully worked out the selling the books in to the first owner step. The big copyright holders don't really like competing with the secondary ownership market. So if enable that too fast they'll throw up roadblocks. Apple got the over billion songs sold before got to the DRM free stage with songs. Folks want the book market to jump to that stage with far few units sold.
For Amazon it could be like a "e-gift card" thing. You transfer ownership of a e-book from your library to theirs. It would be more complicated if folks wanted to sell them but books as gifts... that shouldn't make the book selling folks too up tight. (although with paypal could just settle up without Amazon in the loop. ) Then if it is a "loan" it would be just a free gift over and a free gift back. Also not sure the number of kindles out there is a large enough re-gift market ( although catch-22, this might help drive some sales. "if you had a Kindle I'd would transfer some books I don't want anymore to your library." )
However, often in discussion of things electronic, the notion of wanting to "lend" isn't a real transfer the sole copy but of giving someone access through a copy.
The US code... ( not sure if this is latest, but doubt this subsection has changed)
http://www.law.cornell.edu/uscode/17/usc_sec_17_00000106----000-.html
the owner of copyright under this title has the exclusive rights to do and to authorize any of the following:
...
(3)[\B] to distribute copies or phonorecords of the copyrighted work to the public by sale or other transfer of ownership, or by rental, lease, or lending;
Note the lending. Must books comes with a notice next to the copyright of "All Rights Reserved".
I think these guys (and the publishers) are getting too greedy (predictably) and someone will come up with something that's a better value.
Some publishers are in the business of selling "hot" books. They want to strike before the popularity fades. In that sense it isn't really greed that has the book priced higher when demand is very high and then lower once it fades. Those who are willing to wait a year (or so) until the price drops get to pay a lower fee. Those who have to read it right now or they will just "die".. pay a somewhat higher fee. [ Targeting the "That's Hot", Paris Hilton style, market is why we get more trash. ]
If the higher fee was permanent long after it drops off the best seller list then that would be greed. They should also have much less leverage after the Kindle catalog becomes huge and if they develop better ways folks can find good books that don't have huge advertising budgets. Competition always helps reduce prices.
It will be interesting to see what happens to Kindle/iPhone integration if (when?) Apple releases its much rumored 9"-10" iTablet.
At this point, iPhone isn't a real competitor to Kindle when it comes to digital books. But obviously the game will change quite a bit when Apple comes out with its own device, more similar to Kindle in form factor.
There are no serious rumors about an iTablet. There are tons of folks on rumor boards lobbying for an iTablet, but there is exceedingly little evidence that Apple is working on one. There are things that are twisted into being tablet work, but nothing remotely creditable.
It is up there with the G5 powered iBook.
Anything 9"-10" inches in diameter better have a keyboard attached to it. At which point if still under the low end macbook in price ... would be the new lowest end of the macbook line. (and not good reason why it would be an iPhone OS dervative. )