Except that twitter does go down, so if you had a distributed car that was incapable of hitting a tree it would be an advantage.
The situ with email is that at any moment the system is up but individual nodes may be unreachable or delayed, conversely if twitter is up all nodes are reachable in constant time, but if it's down all nodes are unreachable.
In real systems these two properties are mean virtually the same thing, at any given point in time your party may or may not be reachable with a given latency.
