A pc case is earthed at numerous points due to the way the components are installed ie power supply fixing screws,motherboard standoffs etc.
I would not want to use a computer that had no earth present.
When installing components it is recommended that you ground yourself with a wrist strap connected to the chassis to discharge any static.

Back to carpet cleaning machines,I would have thought that as water and electricity are in such close proximity any external metal parts should be earthed to prevent risk of shock.
The service you have received from Amtech is appalling and the company should be boycotted and the word spread as to their dreadful lack of customer service,maybe your local press may be interested in a story.
The problem with commercial suppliers is they think they are a law unto themselves,a customer is a customer be they domestic or commercial and should have the same rights,can you imagine what would happen if someone at Comet told you to F off?-John