This assumption is hilarious and misinformed. YES, you would sell more units IF you would take 2 days of your engineers time to solve this very simple problem. The vast majority of machine shops and designers DO USE inches and feet and not the metric system. I cannot stand CURA for this reason alone. I have owned 5 Ultimakers and sold 4 of them partly because the software is so hard to use. Most other 3d printer software DOES offer conversion to inches. I'm working on a project right now that would have been set up in seconds on my other printers, but because I'm running it on Cura for the S5, it is a serious problem as the file will not load correctly because it was designed in inches. When making the conversion myself, it does not tell me where it is measuring the vague length and width on a non-square part.
In the end, Ultimaker has a long way to go to compete in the US market and I'm quite certain their arrogance as designers is preventing them from becoming commonplace here.