If the smarts is just a state machine, and the rules are abstracted at the right level, it would not be that hard to support.
"Thick" smartpoints can save on operating cost (infrastructure, personnel, complexity, level of expertise) when your system is "simple enough"
At massive scale, from an economies of scale (all things considered), it may make better sense to go with "Thin" smart endpoints.
The migration between the 2 models is where the art of the design comes in play :) It's an art because it is a decision process involving many players with conflicting and competing goals, decisions, time frames, motivations etc.
It's often not just a "technical" decision
