Every 30,000 is about what I used too. If you drilled down into Steve's information and checked out the "Normal Maintenance Schedule" you'd see that it's the same for wheel bearings either way. Every 30k whether babied, or rode hard and put away wet.
I generally felt that 25k to 30k was acceptable on a daily driver, and that's just about what I ended up doing every time. Chilton's lists it as 24k or 24 months, whichever comes first. Chilton's was pretty much what most of us went by in the old days before we thought of spending 100 bucks or more on factory Ford shop manuals!
Other criteria, pretty much every time you did any brake work, or cleaned out the locking mechanism if they needed it, or otherwise had anything else apart up front.
Any time you have it off the ground you can check the action and see if it needs any service before the normal scheduled time arrives.
Kind of a critical component, so not the kind of thing to ignore.
Also generally accepted that you should inspect and if necessary re-pack them EVERY TIME you got in some water when going off-road. If it got over the hubs, it could get in the hubs.
If lubed and adjusted properly, the front bearings and hub components can and do last the life of the vehicle.
Paul