Even if the implementation is discrete (as all digital hardware), it may be more natural to treat things such as a temperature sensor, mouse position, and perhaps even video as functions of continuous time, values that vary continuously. So behaviors are not a workaround at all, in this sense.
Just as we program with infinite lists etc even though the implementation is finite. In this way, implementations serve abstractions/semantics/specifications, rather than vice versa. See also http://conal.net/blog/posts/why-program-with-continuous-time/ .
- Conal