it's a very common problem and had to do with the manufacturing process like others have already posted. the dash on my '99 Ram was already cracked and broken when i removed it to replace the evaporator to fix an AC problem. i shopped salvage yards and bought a "like-new" dash including the sub-frame, trim pieces, ashtray, cup-holder, and glove box for $275 shipped. it took me about 10 hours to remove the entire dash and replace the evaporator and about the same time to reinstall it...
if i had only wanted to replace the top dash panel i would've still had to remove the entire dash because there are screws holding it in place underneath. if you decide to go that route i'd recommend taking pictures, labeling everything (esp. the wiring), and keeping all the parts/screws together for each particular section.
here's a couple sites to check for parts:
if you can't find what you need from a salvage yard you might be able to buy an after-market top dash panel
or you could install a dash pad
(cheaper & easier) over the top of you're existing dash...