Royce -

You will encounter a wide range of practices among printers. In the ideal world, "they have such a profile." This is a laughable assertion at the majority of printers in the US.

Here's what you'll find:
1) A small minority of print shops are fully color-managed, offering you custom ICC profiles of their proofer/press with an understanding of how it all works and a willingness to partner with you on getting outstanding color.
2) A larger group of printers say they are color-managed, will offer some sort of profile that may or may not work, but haven't a clue about the whole thing.
3) The majority of printers claim they don't use color management, and perhaps are openly hostile to the entire concept. If you want to do the CMYK conversion yourself, and are able to get through to the pre-press dept., they'll tell you to either use a canned PS profile (like SWOP v2 - not a bad solution), or they'll tell you to use the Custom CMYK engine and supply you with the proper setting (like Light GCR, 92%K, 320% total ink - or something like that).

The bottom line is that, unless you're able to shop around for a printer in the first example, you're at the printer's mercy. It's to your advantage to do whatever they tell you, even if it's from the 1980's. There's no reason to spend time telling a non-color managed printer the error of his ways. Whatever works for them will work for you. Communication is the single most important factor in a successful printing job.