The fish is more likely to be stressed to the point that it would be affected by ich during shipping, or even just the drive from the LFS to your house in a small plastic bag, than it would be by regular water changes in your tank. In addition, if it has something else besides ich (that's not the only fish disease you know...) you can identify that before you infect everything else in your tank.
Also, you might want to give people more than 15 minutes to reply before you start bumping the post up. [smilie=wink.gif]