Yes, the new emulsions (t-grain for kodak, e-grain for ilford) have almost no toe or shoulder. Think of the toe and shoulder as areas of non-linear response to exposure. Most film has a toe and shoulder in any developer. Theoretically, if you give film X exposure, it will have Y density. If you give it X+n exposure (where n is just some positive number), then you should have Y+n density. It should be linear. Increase one, increase the other.
But the toe is the area where it's not linear. X+n still gives you Y. The longer the toe, the less response you are getting even though you are increasing exposure. That's different film has different film speeds in different developers (remember that H&D curves, or response curves, are film & developer dependent, not just one or the other). If it's got a long toe, it will be slower since it takes more exposure to get to good shadow detail (out of the toe).
The new emulsions have almost ridiculously linear responses. This gives a wide, even, and arguably unnatural tonality. But technically it's just really, really even tonality.
And films with little to no shoulder are _not_ tolerant to overexposure in general. Think about it - if you overexpose, and the H&D curve is linear even to the top (ie - no shoulder), then it just keeps giving you more density as you expose. It's easy to get to maximum, solid silver as you go up.