Well, maybe. My company introduced a ladder-logic monitoring software package about two years ago that ran on the Jornada handheld PC. It was discontinued about four months ago because of slow sales and the difficulty of keeping up the software releases to run on the rapidly-changing CE/PocketPC/XPEmbedded operating systems.
Oh, and one more reason.... theft rates were preposterous. My demo survived just five weeks before disappearing. I don't know a single sales office who has anything but the charging cradle left.
A clever company called Narly Software offers a limited-utility HMI for the Palm Pilot. I myself use my Palm as a serial terminal all the time.