[jon-wood]

Consultancies like Accenture have a vast army of contract lawyers who'll be on the look out for clauses like that, ensuring that they don't end up out of pocket because a project overran or didn't meet expectations.

That initially sounds incredibly shady, however it's not infrequent for projects to fail for reasons outside the contractor's control. Maybe the client can't make up their mind as to what they want, or internal politics mean funding gets cut for the project and it's terminated halfway through. Big contractors absolutely will sign a contract with clauses around deliverables and timelines, but they'll also refer every little deviation from what's listed in that contract to a change control committee to ensure it's accounted for, and doesn't come back to bite them in the ass.

Mostly you don't want to run a project like that, because as you work through the implementation you find variations from what was originally documented, or new edge cases that need dealing with. In many cases you're better off taking the risk of overspend or overrun than ending up with some software that perfectly fulfils a set of requirements that don't reflect reality.