Let me tell you why I said that. If you connect all the components on the "+" side of the circuit and then put them all in a metal chassis with the "-" side of the circuit being common and connected to the chassis, everything is fine. But if you were to switch the tweeter cable assembly so that the series components were on the "-" circuit path, then the chassis connection would short these components.

Not many crossovers are mounted this way, so it is rarely a concern. But when mounting the HF horns externally, having the crossover in an external box is a good and attractive solution. If the connectors are all mounted on a common metal panel, then this becomes a possibility.