I can not comment on the Elantra specifically as my 2003 only has 17k
miles and they are still fine.  Wheel bearings but in general are a wear
item and need replaced and or repacked at specific intervals.  Rarely do
they "suddenly" completely fail but once they start going bad they get
worse as time goes on and should be replaced as soon as possible.  I
have never replaced any at a specific interval, only when they make
noise while driving or when they have play as I check them pretty much
any time I have a tire off for something.  I ride share to and from work
in random cars daily, I've been in everything from a Ford Focus to 7
Series BMW's with bad wheel bearings.  It is actually suprising how many
people drive around and do not notice or question the noise.  Maybe they
are used to it as the noise gradually gets worse as the bearing gets
worse.  I think it is very obvious by the wah wah wah sound when driving
anything about 20 mph.  Sometimes a tire can cause the same noise but
can be isolated if you roate and the noise is still from the same place.

How much did you pay to have yours replaced?