I have spent countless hours debating the value of a physical book versus a digital copy of the text. I have a literature degree and I took a number of classes which dealt with publishing practices, the history of print, the rise of digital and other relatedly things. I have read essays on the topic, attended guest lectures, listened to other students argue in classrooms and watched executives for publishers and digital companies argue with experts on literature and typography. And I have found that the argument against e-readers are mostly people stretching to find things that are wrong with them because they like the way books smell.
I don't think there is anything wrong with liking the way a book smells or any other aspect of its physical form, and there are things that physical books do better than digital copies, but there are also things digital copies do better and there is room in the market for both. Digital copies are not a replacement for leather bound collector's editions of your favorite book. They are a replacement for paperbacks. I have paperbacks which my father read in college and the majority of them are already worn and brittle so arguments about lifespan are really moot. They were not made to last, they were made to be inexpensive and portable.
My biggest problem with arguments for books as objects is that it seems to accept as fact the idea that when I buy a book I am buying an object and not ideas. This was not always so, it was successfully argued by publishers 200 years ago, and led to our current intellectual property laws, but I don't accept it as fact. When I buy a book I am buying it for the intangible ideas it contains. Arguments which centered on there being nothing there, or the experience of reading being diminished without a physical book trouble me because they seem to buy into this. It ideas and the words that form them which make us fall in love with a book, and those words and ideas still exist on an e-reader.
The rise of digital technology may scare those who love physical books, but it needn't, for one thing I think that it will do good things for the future of physical books. Print on demand technologies mean that a book need never go "out of print" enabling you to find a copy when you want one. I think that as more people get e-readers the market for nice physical copies will actually increase, and the offerings for this segment will also increase.
The cherished memories of passing a book from one generation to the next may slip away, but as I said I think nice editions of books will still exist. If passing a physical book along does stop, well that tradition had a start, people still loved each other, and shared their knowledge and experiences before there were printed books, and they will continue to do so after.
As far as obsolescence, that is a real challenge for digital formats, but it is one that people are tackling. People back up their copies, as linked above there are format converters and "the cloud" means that even if I lose *my* copy a copy will still exist and I will be able to find it.
I don't think that we are casting books aside for digital copies simply for the sake of "modernity," e-readers do a lot of things better. They make a text inexpensive, portable, searchable and allow me to look up new words as I read. These are things that print can't compete with, and so like manuscripts gave way to print, print is giving way to digital.