According to the South African National Treasury, not only are the stadiums ahead of schedule, they aren't projected to go over budget. While the norm in journalism these days is to cast doubt on everything having to do with the World Cup in South Africa, it's easy to see why the government needs to come out publicly and at least show confidence that things are running smoothly.
Regardless, there's just too much at stake (see Venezuela/Copa America) for the World Cup not to come off in three years time. This is Sepp Blatter's baby, and he'll be damned if it doesn't come out an organizational success.
South African Stadium Construction Ahead of Schedule [Bloomberg]