We often get asked before people purchase and after they purchase natural stone tiles is how they will wear over time. The truth is like anything else, they will wear depending upon the traffic they get and the general amount of hammer they endure. Travertine tiles have their own issues, as travertine has a honeycomb structure and small pits and holes can form over time. This is perfectly normal and can be easily repaired with a filler called "Jolly Mastic". You can get it in various colours and can be used to repair all types of natural stone, not just travertine tiles.
Other natural stone tiles, like limestone tiles and marble tiles, can be easily restored to their former glory by specialist restoration companies like "Imperial Floor Care" in Manchester tel 0161 431 4743. Below is a message we received from them not long ago about an interesting new system for polishing travertine tiles.
We have just launched a new marble polishing and restoration process that only uses water to give the results of the attached pictures. No harsh polishing powders and seals are used. The system is extremely fast and means we can charge considerably less. We do a lot of work with Topps Tiles polishing stone for their customers, but also do a lot of work, taking out the odd scratch out here and there from damage tiles which have been laid. The pictures posted here were supplied by them. Even if these guys aren't in your area, there will be others like them that are. Try locating somebody on the tta.org website (The Tile Association) whom we are members of.