With multiple competing options (some in the cloud), surely one of them will cater to the old UI that uses the arrow keys.
Specific to accounting, my anecdotical experience has been that many accountants don't like change unless it makes them more productive. If it's confusing or has a large learning curve, expect lots of complaints and resistance. I upgraded a few with new computers, from Win98 to Vista, and from Office 2000 to Office 2007. The "ribbon" UI was so terrifying to them that they literally unplugged the new computers, plugged the old ones back in, and used them for 9 more months before they finally crapped out.
Any type of manual data entry needs to be done really fast and accurate. Keyboards are better at this than touchscreens in most cases. Touchscreens will have to become more keyboard-like to compete (this is going to begin happening soon, but we're a few years away before it becomes good enough: http://cnettv.cnet.com/senseg-demos-prototype-touch-feedback...).