Cnet's Larry Dignon points out that the Kindle DX is not economical for students.
In year three, that student will start saving money via the Kindle ($1,464 on paper textbooks vs. $1,239). The big caveat here: I didn't include the used book market and assumed that the Kindle DX still functions well. Another big assumption: All the textbooks you'll need will be available on the Kindle (not likely). If Amazon can cut a student's textbook costs to $100 a year, the case for the Kindle DX would obviously look better.
In a nutshell, Amazon is trying to make a four-year total cost of ownership case to an audience that just doesn't have the attention span.
The reason Kindle DX doesn't have a WiFi option is because it would make Amazon less money than selling them hundreds of dollars worth of WWAN up front.