I no longer have a SCAN button in the Print&Scan System Preference. I am using an HP C6380 and an HP C4700. I was able to scan until the latest Mtn. Lion update. Any fixes (PS image capture doesn't work either)
iMac, OS X Mountain Lion (10.8.2)
I see the C4700 (but not the C6380) in the supported printer list under the "Printer and Scanner Software" link near the top of the Mac 101: Print article here:
http://support.apple.com/kb/HT4670
But from that reference, the C4700 does not purport to support scan on Apple's software, only print.
... so my guess is your printers are aging, and if you want to find more support, you would have to check HP's website directly.
HP website doesn't have Mtn Lion Dirvers. However, I moved the printer from the Airport to the iMac usb port and it works find now.
With the latest update to Mtn Lion, My HP C6380 no longer has a scans
