No, definitely not a myth.The steel cases are also supposedly harder on extractors
A big, fat myth.
The problem is not the case material. While there is some debate as to whether or not the steel case is safe because of its reaction to chamber pressure, the worst case malfunction caused by the material is a torn case head. You may also hear a caution about steel being too brittle to make a good case web, but I have yet to hear a single word about a blowout from that.
The problem is geometry. The ammo you buy today ain't your daddy's .45 or 9mm. The rim geometry standards have changed periodically, usually in response to metallurgical challenges. The fact is that a Wolf .45 rim is very different from a WWB .45 rim. Hold the two cases next to each other and you'll see it. It's not that Wolf rims are out of spec, it's that they're using a different standard. Extractor design has been tweaked slightly to accomodate the rim changes.
As a result, a 1911's extractor nose can, and frequently does smack into the case because of the shorter, steeper rim taper. There is a way outside chance that this could blow a round, but that would require an astoundingly overlength extractor nose and a really weak case. More likely, the extractor nose smacking the case will push the extractor farther than it should bend during feeding. This can work harden the extractor, and cause it to crack.
This sort of problem affects different guns differently. On a pistol with an ordinary external extractor (I'm looking at my kel-tec as an example), there is no extractor nose sticking out, so it's not such a problem. On a gun with an internal extractor that has a pretty long nose, like a 1911, it can cause a problem.
So, do all 1911s suffer from this problem? Absolutely not. Extractors vary greatly from one manufacturer to the next. The Springfield factory extractor I pulled off my pistol is far narrower than the Wilson model I installed in its place. The pad is machined differently, the radius on the hook is different, and, of course, the nose is a different length. The safe bet for good extractor life is one of two things: either avoid Wolf ammo altogether, which is not financially viable for some shooters, or inspect your extractor, its interface with the rim, and fired casings for evidence of a problem. A small relief cut (VERY small) will likely fix the problem.
If anyone requests, I will happily break out the camera to document all of this.