<p>Do moderate or large projects ever not require an architect? I have worked on a number of projects where the development company involved has choosen not to assign an application architect. Either the software is built organically and with little concern for design or the design responsibility falls to senior developers.</p>

<p>The motivations for not having an architect range from cost considerations to believing that the development methodology makes the architectural role unnecessary (this argument could be made for agile development). Some open source projects work on the principle of collective contribution rather than development with architectural leadership.</p>

I'm going to have to use an analogy here utilizing houses.  Not too long ago (relatively) people could build houses without an architect or architected plans.  They cut down some wood, used learned skills to cut and plane boards and built their houses.  Cathedrals, castles, etc....they had architects and engineers, sure.  But the vast majority of the time it was people using skills passed down to build a house.
These houses did the job but didn't last as long. They might be a bit leaky, they might be hard to improve, etc.  But it's easy to use water to level your foundation and then add wood.
Modern day houses have infrastructure to plug into, codes that have to be met, etc.  We need our housing designs created or approved by an architect before they can be built. The architect makes sure everything's up to snuff and that the house will stand and be habitable.
Applications are no different. We are not living in a world where complex structures can get away without being architected.  Sure I can write a database for my library as a trivial exercise; I can also build bookshelves for my library without getting an architect involved.  But once you get beyond simple structures, you should absolutely make sure somebody is paying attention to the bigger picture -- whether your structure (house or application) is going to do what it needs to do, whether it plays nice with others, and whether it meets the rules set upon its construction.