It depends on the publisher, most of them from what I've seen, the marketing budget is however deep your pockets are. I've gotten a few things out of Xlibris, for example we had a bit of a tussle last July and they sent review galleys to 5 outlets of my choice but then I found out they just sent the copy they didn't even include a cover letter, under the rationale that the magazine or website would know what the book is there for.