That's just the thing - These guys aren't even worried about flanges, they just crawl under your truck with a sawzall and chop it off. Then they don't have to worry about rusted bolts or anything sticking or stripping. They definately have some huevos making all that noise and not getting caught. I mean, I could see maybe a pipe cutter, but they are definately using sawzalls.
I guess it all depends on what kind of area the trucks are in. In our area, they wouldn't use sawzalls, because the noise would wake people up, and here, they'd come outside. I know of one case in Vacaville so far, and they took the nuts and bolts of the cat, instead of cutting.