I'm also a fan of cartridge bearings. I can't see any reason why they are the exception rather than the norm except that they a) probably cost more to manufacture and b) pro racers don't use them due to a ever so slight loss of efficiency.
You don't always need to replace them to service them. Check out
this thread on how to renew the grease while leaving the bearing in place.
If you do decide to replace the bearings, just be careful to press on the proper inner or outer metal race when installing them. If the bearing is being pressed into something, press on the outer race. If you are pressing something into or through the bearing, press on the inner race. There are special tool sets made to do this but it's not hard to find sockets, washers, bushings, etc that you can use with a vise or threaded rod to push them together.