I also don't know what these prices include. on the French railway site I see that the one-way, second-class fare from Venice to Milan is about $33. I assume Raileurope is including a reservation fee, but Raileurope has always been much more expensive than if you bought the tickets in Europe. A 5-day, 3-country(continental Europe + Ireland) selectpass in first class costs $356; a 5-day, 3-country(continental Europe + Ireland) youth selectpass (under age 26) in second class costs $249, and it may be worthwhile buying individual tickets, rahter than a pass. I've never had any problems getting reservations after I arrive in Europe, except in Poland, providing I was flexible on departure times and even on routing. Sleepers are more of a problem, however. I almost always just get on a train, albeit in first class, and just look for a seat. I may have to change seats diring the trip if a passenger with a reservation pops up. You can make all your European reservations in Paris, by the way; you needn't wait until you get to Switzerland or Italy. If you are really worried, I would get the tickets and reservations by mail from Europe, not from the Raileurope office in the U.S. The German railway (www.bahn.de) is very reliable and will send tickets (also for foreign trips) to the U.S., but their site doesn't give the price for foreign trips; for that go to the French railway site (www.sncf.conm), but they have problems sending tickets to the U.S.
Enjoy your trip, and don't get too worked up about being stranded; there is always an alternative routing or timing.