Can't confirm that. My Launchpad can delete Apps in 10.8, only apps from the store of course (as in 10.7).
I have the same issue, cannot delete apps from launch pad. I can only delete apps I downloaded and installed manually.
So how exactly are we meant to delete apps we download and install manually?!
Why is it always so difficult with Apple?
How did you delete an app before launch pad ?
That's how you delete an app that wasn't downloaded from the appstore.
Open Finder and go to Applications tab on the sidebar. You can drag apps to the trash from there.