Interesting. It makes sense that businesses want to be associated with strong brands. Using an lesser known tablet brand at their point of sales / customer interaction tool might make them look cheap.
Or they literally don't realize there's any other tablet out there--other than Kindle Fire, which in their mind doesn't run small business apps.
People associate Kindle Fires with "cheap tablet for their kids." And cheap they are--when they break, it's actually cheaper to buy a new one than to replace a cracked screen on an existing one.
I guess using an iPad could make the consumer feel safer. Than again a "Pro" looking case for the Android tablet might also do the trick.
Swiping your credit card into a dongle attached to the audio jack of an iPhone/iPad. Seems legit.