It's common for a printer to suggest an optimum (or native) resolution for their process. Peak Imaging for instance state 254dpi for one of their product lines. I wouldn't worry about it over much.
There are other issues with printers such as the colour space of supplied files, and it seems that often their default is to apply auto adjustments (white point, black point, etc) - remember that they get sent a gamut of quality of work. I have the impression that some may also apply some sharpening! I would prefer to choose a printer who allows an option of non-intervention - ie they print the file as sent if asked to do so. It's up to you then to set up the file to get the best result (the human eye is better than any automated process, and only you can know your full intent).