There is no doubt that cartridge bearings have taken over the hub market now and after using them for over 20yrs, they are often seen as less hassle for most users than a fully adjustable loose-ball design. If a bearing wears out, it can be driven out and replaced with a simple press set. Or, as most people do nowadays, just take it down the local bike shop and get them to do it. Time taken to change bearings could prove less over the lifetime of the hub than time taken to fiddle with preload adjusters and "cones" on older style hubs.
We are frequently asked what hub is "better" than the rest. As a hub's rolling performance is only as good as the bearings, and as seals and freehub mechanisms vary widely, it is a difficult question to answer. There is no doubt that Chris King's "surgical grade" bearings are really good and we have yet to change a worn out R45 bearing in 6yrs of using them. But changing bearings in the Wheelsmith hubs, for example, takes less than 10 minutes. Less than 5 in a workshop with a hammer, a drift and a bearing press (£20 or even free if you make your own with a bit of 10mm threaded bar, 2 nuts and few washers!).
The frequency of bearing replacement is directly proportionate to bodyweight, riding duration, weather conditions and frequency of maintenance. If you take that into account, you shouldn't be dismayed when they wear out "prematurely". If you are a heavier than average cyclist (>85kg), expect bearings to wear out more frequently.
Should you need to replace bearings, they only cost between a few pound each to around £15 for Japanese SKF Grade1 units. Chris King bearings do start about £35 each, it has to be said.
Freehub bodies wear out from 2 aspects; bearings wear as explained above, and also cassettes will wear gouges in their soft alloy bodies. See the FAQs for this - it is normal, especially with Ultegra and DuraAce cassettes which were originally designed for a unique Shimano freehub design.
With most hubs, it is usually cost effective to replace the bearings alone if the body is not too worn. Campagnolo pattern freehub bodies do not gouge and if you are using a high-end SRAM cassette on a Shimano body, the same applies. If the freehub body bearings are knackered AND the splines are worn (gouged), it is time for a new freehub. Wheelmith freehubs are £35, Chris King about £120 - both incuding bearings.
So, keep the hubs clean and greased (or oiled) and they will perform perfectly until the little cartridge bearings wear out.
From years of experience with all types of wheel and all types of ownership, it could be said that the money should be spent on quality training wheelsets, keeping race wheels to a bare minimum. If you are spending countless hours in all weathers on all types of road, you will need a heavier duty wheel design and hub type than something you are only on for 2hrs every other week. Chris King hubs aren't really going to make you faster (although some say they "feel" faster) but they have obvious gains for year-in-year-out high mileage use. Same goes for Hope and DT Swiss. However, it is foolhardy to expect a stripped-out race hub to be as durable.
Many customers want a wheelset on a budget that does everything - commuting, training, turbo-training, racing, even a bit of TT use. This always ends in disaster unless you put the money into the wheel design and hub quality.
A couple of things to note:
you can kill a hub with kindness. It has been known for a customer to be constantly fiddling with the freehub, taking it apart to clean it and regreasing far more than is necessary. This will wear the bearing contact points on the axle and you face a much greater chance of losing or displacing tiny springs or circlips inside. Spring-loaded pawls need careful consideration. Degreasers and excessively penetrating fluids such as GT-85 will shorten bearing life span.
no freehub seal is 100% air/water tight. It faces friction between at least 2 rotating surfaces. Dampness will get into the freehub and hub bearings and if you are leaving the wheels dormant for any length of time make sure they are dry around these parts. Even those "surgical grade" stainless bearings will suffer if neglected, especially from salty road water.