Why software development is not same as building bridges

I came across a very old post on itmweb titled: Why is software development not viewed as R&D, but more like manufacturing? (http://www.itmweb.com/ubb/Forum3/HTML/000010.html).

One of the replies to the post argues that software development is similar to engineering projects like building bridges. That view couldn't be more off.

Equating software development with building bridges doesn't make much sense to me. For one, building bridges needs a lot of upfront design because you cant change the bridge once built. Software continuously undergoes changes. There is very little that can't be changed / rewritten in software. I would also agree with diltondalton - in that designers and builders of a product are the same. Another way of saying that is that in software, the worker on the ground will have to continuously create as opposed to the very mechanical nature of the their equivalent's work when building bridges. In fact, you don't want the workers building bridges to think. Thats the designer's job.

I would also agree with the spirit of the original post. If you are pedantic, you would argue that it differs from R&D in a manufacturing company. But it most definitely is not the same as manufacturing. As we try and bring in more and more lean manufacturing practices into software development, that becomes all the more clear.