Absolutely not; many successful authors aim for particular presses, and even specific editors, long before they begin to write. Here's a simple example: if I assign you the task of building a ship to sail to a destination, you would logically ask "Where are we going?" One takes a different sort of vessel to Belize than to the Arctic Circle. In many ways a book is a vessel -- it is a paper repository of thoughts expressed as words that somehow must find its way into the homes and hands of readers. Many never complete that journey, but happy is the ship builder whose literary vessel sails true. Choosing a publisher early makes sense in this analogy, because different slants and styles of books work at different publishers.
Typical authors, especially first-time academic authors, write whatever they want to write, and then go knocking on doors trying to find someone to publish it. Seasoned authors, however, are aware that presses have specific characteristics, and that the more one knows about presses and even individual editors, the better the chances that the book will communicate with those professionals, and through them to a precise audience. Also, many editors see themselves as partners in the shaping of the final book -- their jobs are intellectual, not clerical, and they are there to help you craft your work to fit in that artful collection known as their list.
How can you get to know presses? The simplest way to start is through their official self-representation in their catalogues. Publisher catalogues are often works of art in themselves (I collect attractive covers), and they reveal much about the identity of a press over time. If you want to see a lot of them at once, make friends with a bookseller and ask to view back catalogues. Many publishers have good web sites as well, and you can peruse these sites for more than a simple roster of authors and titles. You're searching for editorial identity -- what makes one house distinct from another. In the case of university presses this is often an extension of the university's own stature and image.
I have chosen a press, although for the purposes of this online journal I won't name it until/ unless my proposed book gets in. What I will say is that it is a press where (1)I have visited in person; (2) I have studied its catalogues going back ten years; (3) I have chosen a target editor based on her/his stated editorial interests and upon the output over time that I respect (this is so important -- you need to know what an editor has done -- look at the final product and read her or his books!); and (4) although it is a university press, it has a strong track record of books that have been successful in the big bookstores. Only a handful of university presses fit this last description.
Whether or not my book makes it in at this press, I am improving my chances simply by knowing where my boat is supposed to go. If I do get in, it will be partly because research and forethought pay off. If I don't get in, I have still improved the chances that my book will find a home elsewhere because I have crafted it to actually fit a stated and successful editorial need.
(Hint: It's not the press in the photograph!)