Good Mornings vs. Romanian Deadlifts

It's seems to me that the mechanics of both lifts are the same except for the bar placement. However, the since you're holding the bar in your hands for the RDL you're obviously working some additional muscles. That leads me to conclude that you get more bang for your buck with RDLs. But the guys at Westside are big advocates of GMs and they are some of the strongest guys around. Any ideas on why they prefer GMs to RDLs? I can't help but feel that I'm missing some important difference between the 2.

It's not really the same. GMs create a longer lever arm, and make your back work harder. Another difference is that the bar doesn't stay over the mid of your foot which makes the hip extensors work harder.

GMs are one of the best ab moves you can do and they'll carry over to your low bar or PL squat. Generally speaking. There's a school of thought that says deadlift-favored bodytypes (dolicomorphs like myself) get more out of RDLs and other pulls than squat-favored bodytypes which benefit more from squat-type movements.

I do both as they are both effective accessory movements.

I like GMs a bit better at the moment. A low bar GM is pretty similar to a RDL but high bar is much harder, especially on the abs. If you need a bit of extra grip work though RDLs are great too.