All of our fixtures come standard with a chain. Why chain and not a rod? Two reasons. The first reason is flexibility. Using chain allows you the flexibility to add or remove links of chain to quickly change the hanging height of a chandelier. This is especially useful if you're installing in a space where you're not quite sure what the ceiling measurements are or if you're note quite sure how high you'd like to suspend your fixture. There is a bit less flexibility if you use a rod because the rods are a fixed length. Many chandeliers may actually include a set of rods (3 or so) that screw into one another and allow you to choose how high to hang your fixture in foot-long increments.
The second reason to use chain instead of a rod is cost, and a foot of chain (unless you want something totally fancy) typically costs less than a foot of rod. Also, with many chandeliers, you may end up paying for rods you don't actually need, so one way we use to reduce fixture cost is to provide items such as rods as separate purchases instead of creating an overall higher cost for all of our clients.
That said, if you're still unsure how high you'd like to hang your fixture and you still want the high end look of a rod, you can use both. By simply adding a loop to the end of the rod, you have the opportunity then to attach the chain between that loop on the rod and the loop on the canopy. Boom. High end. Flexible height. Done.