I get pork picinic roasts at our Kroger (Fry's) market here in Phoenix. Pork "butt"...
...is higher up and contains the actual shoulder joint. Picnic roast is the distal end of the front leg, and has a portion of the shank (narrow end) on it. As with your experience, it always has a ton of skin on it, going all the way down the shank end.
I see the very same cut of meat called the Pork Butt Roast, Pork Shoulder Roast and Boston Butt. Here, they are interchangeable. It is the high shoulder cut.
NOW, if I want an actual REAR LEG cut of pork that is not cured and made into ham, I go to the ASIAN butcher at the local Asian market. His meat case has whole, raw, uncured hams, or back legs, and they are HUGE. He will cut to order, so it is a good thing.
Michael