Modern vehicles do not have greaseable wheel bearings for the most part, so people don't think about it. I have replaced my sealed wheel bearings with greaseable bearings on the front of my TV and from here forward will be repacking the TV and TT every 2 years.
My TT is going on its 3rd season and I pulled 1 of the hubs off a few weeks ago and was shocked at the shape of the grease and bearings with only 2 full seasons and approx 7K miles on them. I have all new Timken bearings that will be going in sometime the first two weeks of June before any long trips. They where not shot, but the grease was overly dark and the rollers where very loose in the cage, not what I normally see on good bearings.
For reference my Al-Ko owners manual says to repack every 12K or 12 months, but that can be extended with proper use of the ez-lube hubs.