Nice timing for this topic. I don't have an answer, and this is mostly just rambling, but I was thinking along the same lines this weekend:
I always cook Picnics, because that's all I can find in stores by me... usually about 12-14 pounders. Summertime it's easy to catch them on sale @ $0.69 a pound. Just this past Sunday I was doing my last round of shopping for Memorial day, up in a different part of town. Stopped into a Wal-Mart Neighborhood Market to see what they had. I found both Picnics and Butts in the 8lb range. For a test I picked one of each, the Picnic a little larger to account for the skin I'd cut off, and I planned to season and smoke them side-by-side for my own test and find the definitive answer.
Well... when I cut open the Butt bag I was hit with a pretty foul stank. Like strong enough my wife smelled it across the kitchen. A quick rinse under the faucet didn't help things, so I took it outside and chucked it straight in the trash. The Picnic smelled just smelled like fresh clean meat, and the end product turned out dynamite as usual. I'll give Wal-Mart the benefit of the doubt that they let one bad one slip through. No test for me this weekend, but I plan on trying again in the near future.