re: "...Seems to me that would be the whole point of using synthetics: not having to change as often...."
Well, here's another opinion -- the whole point of using synthetic is to better protect the engine against wear, so it lasts longer. An awful lot of oil changes (even at synthetic oil prices) will NEVER come close to the cost of an Mercedes engine lower-end rebuild (i.e., cylinders honed, new pistons & rings, bearings, etc. -- a BIG etc.). Since even the timing chain is protected by the oil quality, even that is better off with synthetic.
So, change oil (and filter) just as often as with conventional oil.