It is called boar taint:
http://en.wikipedia.org/wiki/Boar_taint It doesn't matter if you cut off the parts after you kill them. I've wondered that about the wild hogs as well.
I have to share a story about pig hunting here in MN last year. I was out working on the shooting range about mid September. Look up and see a large animal moving along our fence line about 200 yards away. My first thought was a bear, but when it got out of the brush I could see it was a pig. Just behind her was a litter of little ones just scooting all over. Evidently one of our Amish neighbor's pigs got loose and farrowed out in our corn field. She had evidently been out there awhile, there was probably a couple acres of corn knocked down.
We asked around, but no one wanted to claim her, probably knew that there would be damages, ha. She had definitely went wild and there was no getting close to her. She had 150 acres of corn, swamp, and woods to hide in. We thought about trying to trap her but decided to limit the damage and just shoot her. We had her processed at Miltona Meats and she was tasty.
But the little ones were still out running around. My DW and I went out one afternoon and came upon them sleeping in a pile on the edge of the field. I wish I would have had a net, but I did manage to grab two. Later I caught one more. But they wised up and I got busy with other things. My buddy saw them off the deer stand a couple times and we ended up shooting 3 more after deer season. The neighbors shot four. Those little pigs were probably a month old when I shot the sow it was amazing at how well they survived and thrived.
The three we raised ended up being a boar and two sows. One sow had a litter this last summer, we ended up selling them all except for one sow that has an appointment at Miltona next week.