The point isn't that taxis don't have credit card terminals. It is that people often state that the terminal is nonfunctional, defeating the purpose. In Baltimore, this was the norm; I suspect Manhattan is better.
http://www.nyc.gov/html/tlc/html/passenger/passenger_creditc...
>What if a driver says the system is not working? The passenger should note the medallion number and go to 311 Online. Drivers are permitted to work with a broken system for up to 48 hours as long as they have reported the problem and are awaiting repair. Almost all (90%) system repairs must be completed within six hours.
And there isn't much you can do about it except threaten to complain and hope the taxi driver relents and lets you use it.