I just replaced the ball joints (non greasable) on my E250 van, at 114,000 miles. I had noticed that the front tires were angled, but not enough that it concerned me, as I knew it was gonna cost a grand to fix. My wife drove the van, and wouldn't let me have it back without replacing them.
Now, the alignment shop said the ball joints had play in them at 30,000 miles, and they needed to be replaced. Ford said they were within spec, and would not replace them under warranty. Note the difference in mileage, 84,000 miles from the time the alignment shop wanted to change them until they were changed, and I would have probably ran them another 15 or 20K until it was time for new tires.