Brian, first, if that grout looks new, it probably is, and would have been redone to help the sale of the home. That could mean it was done by the previous owner and not by a pro. If the grout is unsanded, the space between tiles should be pretty narrow, less than 3/16". If the grout is mixed too wet, or is cleaned with a wet sponge too quickly after installation, it will weaken the adhesion. It also sounds like the grout was probably not sealed, which I'd recommend highly for a work surface such as this.