A couple of reasons
1. Its looking like a toss up as to whether Bob starts for Russia and there are negatives either for either outcome. If Bob gets beaten out by Varlamov we could see some rust due to him not playing, and this also could cool off his play in general. Alternatively if he wins the starting job that's alot of extra work for Bob which could affect him down the stretch when we need him most.
2. In addition to Bob we also have a few other players going to the olympics (Nikitin, Tyutin, and Anisimov) who all will have extra work loads and have a chance (albeit very small) of injury)
3. The olympic break is a momentum killer for teams. The last month and a half the jackets have been on a roll, but this break is like someone tossing water on a fire. It stops all the positive momentum the jackets have been building.
It may seem a bit far fetched, however our most important player is Bob and as Bob goes so we go, therefore anything that can negatively affect Bob's play can negatively affect our chances of making the playoffs.