In some areas, Trenitalia does provide bus service from the train station. On one of the runs from Siena to Lucca, there is the #8 bus that goes back to Florence from Siena to pick up the train to Lucca. The term ES*Link in the train category column is usually a bus. True, the bus picks you up at the train station and true, you could easily take a train back to Florence from the same station. However, I have seen this #8 bus run a few times as I look up schedules for my postings. You will occasionally see a Trenitalia bus (probably a leased SITA bus) from Siena to Chiusi as well when there is a train station at each location. There are arrangements like this in Switzerland as well. Also, with you being local to my area here in California, AMTRAK does a ton of bus runs out of Sacramento.