Pulled both my unit bearings this week. Both 137,000 on em(OEM, orig. ) , very little grease(on needle set) not much sign of them having had much, and both stub axles where golden.
I'm sure its not the rule. I haven't river crossed and ditch dove a bunch, but every year, seems a bit to often for myself. Think the amount of time spent in 4 wheel drive makes a huge difference. Love launching in 4 wheel and flipping the switch for some tail slapping good times.
Enjoy all.

 

I say annual because you can grease the hubs through the abs hole, caliper slide pins and front end zerks at the same time. To each his own though. Do what works for you.