Apple does not replace the glass or display. Apple will sell you a replacement iPad for about half the original price. The replacement will have the remainder of any Apple warranty left on the damaged iPad.
For perhaps a less expensive replacement of the damaged part look to 3rd party repair shops. Replacing the part will likely void any remaining Apple Warranty.
Apple's Limited Warranty http://www.apple.com/legal/warranty/ for iPad excludes coverage for damage resulting from accident, disassembly, unauthorized service and unauthorized modifications.
Apple will provide a replacement iPad for:
iPad model Out-of-Warranty Service Fee New iPad $299 iPad 2, iPad $249
You can get the glass replaced at 3rd party repair sources for less $, however, the Apple warranty will be voided.
iPad Repair & Screen Replacement Services
RepairZoom iPad Repair