Cash is still universally accepted, but it's probably impractical for the hardcore amongst the hobby community to carry around such a massive wad of twenties to satisfy all of their purchasing goals at a show like Springfield.
Personal anecdote here - I had a brief moment of insanity where I considered buying a brass locomotive. The price was way above what I was willing to carry in cash, I never carry my checkbook with me anywhere nor do I use "no brand" ATMs, and the vendor did not accept credit cards. Alas, no sale for him. I took it as a sign that it was not to be, which was confirmed later that night by my wife's reaction when I told her I'd even contemplated such a purchase!
Good show this year. Can't recall the exact number but something above 19,000 attendees over the two days.