Hackathons are the opposite of "how marketing people think software is made". They are the essence of the process of development with the decoration removed.

Dave must not have been to a good hackathon. I've personally been involved in hackatons where we created what went on to become a commercial product in under a day. The code written during the hackathon may not have been part of the final product, but the creation of the product (what it is, what it does, even much of how it looks) was the result of the hackathon.

I have the diametrically opposite view of Dave in this case - hackathons are exactly the tool needed to obviate the need for months of wrangling with "marketing people". Instead you can go directly to a tangible product that can be touched, tested, and discussed in a meaningful instead of abstract way.