I agree with the parent and grandparent comments.

That said, when I was sponsored for an E-3 visa by a US company the recruiters made it clear that my position was permanent (subject to performance) and that the company would sponsor me for a Green Card.

These representations were contradicted by the legal documents I presented in my interview at the US consulate.

Nonetheless, I can imagine some employees on these sorts of visas might take their employer at their word and plan their lives accordingly.