Sometimes changing the fluid and filter brings about transmission problems that previously didn't exist. The new fluid is thinner than the old sludgy fluid, and with the less pressure running through things start flaring up. Most likely the problems would have been an issue in the near future anyway.
This has been 2 out of 50 or so cars that have had transmission services dealership over the past few years that drove fine before, but not after the fluid change. Both were imports (Jag XJ8 and Mercedes E320), both "sealed for life" and we used the OEM filter and fluid.
Overall, I'd take a 4% chance versus what would most certainly happen eventually if you do nothing.