And you are right, it's much harder for HAL or KBR to go off the rails on an oilco than with the USG.  These guys are great at cobbling together thousands of people and making something happen.  However, they don't always have the best designers/strategic thinkers as they hire and fire with the workload.  The oilcos have a lot of their own people who've had to live with the equipment from prior projects and bring them in to design the systems and ride herd on the construction.  

And oilcos are smart enough to negotiate fixed price deals or at least penalties for non performance.  Even then, unforseen circumstances blow project budgets all to hell.  Witness Sakhalin doubling on Shell, though I'm sure some of that was optimism to get the project approved/funded.