Well, the roc entry does specifically say that this is a roc's favorite food preparation technique, so let's make sure it's actually possible.
The Snatch feat allows creatures to start a grapple with particular attacks as though they had the grab ability. Of course, your roc already has the grab ability! So it doesn't need Snatch to pick up enemies.
The Snatch feat also permits flinging, which acts more or less like a bull rush (causing enemies to move involuntarily). You only need this if you want to launch your enemies horizontally from your roc's current location; if you just want to drop them vertically, you can do that anyway, just by ending the grapple (unless your target has somehow managed to reverse the grapple on you; not very likely against the roc's CMD of 37).
So the only impediment to this plan is that, normally grappled creatures (such as a creature using the grab special) can't fly, because they can't move. You can use the special wording in the grab ability to try to hold your target in just the talons, but that reduces your roc's CMB to +9, which is... still pretty decent, actually. That's probably enough for your roc to keep wimpy characters grappled long enough to carry them 200 feet into the air, and then drop them. Stronger characters with better CMD will probably get dropped halfway up though, when you botch one of your rolls to maintain the grapple. It takes 5 rounds to get up to 200 feet, unless you have a handy cliff to jump off of (not an uncommon feature of roc territory).
Note that holding with a single limb doesn't appear to reduce the roc's CMD against a target actively trying to escape the grapple; I think this is an oversight, personally, and it should probably have the same -20 penalty, but it should also add +4 to the roc's CMD for the same purpose. It probably balances out.
