For many comic book readers,the monthly floppies or trade paperbacks are plenty to occupy their time, but there's a enormous market for original art, and for those with more dispensable income. Unfortunately,that leaves another portion of the audience out in the cold, hence the rise in popularity in oversized, or deluxe Artist's Edition hardcovers and process-wealthy books,that scan the original art in incredibly high resolution and package it in affordable ways.
Source: blastr.com