This is just an attempt to kill the used book market. As it is, textbook revisions are introduced at a rate far higher than actual changes in content; all in order to make older used books obsolete. The entire textbook publishing industry is a sham. Look at so-called "international" editions - these are often identical to the US version, except maybe for physical differences (lighter paper for lower freight cost, or b&w instead of color to make it cheaper to print) or perhaps minor changes in language due to localization. Yet these books are not meant for domestic consumption even though they are perfectly capable of doing the job at a fraction (often 1/4 to 1/2) of the cost of an official US edition.