I'd have to disagree with that, Chubby. There are all sorts of good reasons to grow your own. For instance, there are "pumpkin" varieties (horticulturally speaking, pumpkin is a meaningless term) you might want that are just not available in cans of puree---most of which are hubbard squash anyway.
For instance, this year I'm growing Flat Tan Field pumkins---which at least one famous pastry chef considers the best culinary pumpkin you can get. But the only way to get them is to grow them yourself (or hire somebody to do so for you).
Calabrase, the small white African pumpkin I had hoped to get this year, is a similar case in point. It is essential to many African dishes. And, while Butternut can substitute, I'd rather go with the true gelt if I can.
In my experience, pumpkins are a low-maintainance crop. For most people in the U.S., squash vine borer is the only pest they need to particularly watch for. And that would be the same for any winter squash. Other than that, the only thing I do is train the vines to grow in the direction I want them to go. I don't even weed much, in a pumpkin patch, because the vines serve as a living mulch---one of the benefits of a Three Sisters planting, btw.
For those into the locovore movement---as more and more people are--- processing is a requirement, whether you grow your own or buy whole, locally grown pumpkins. So that part of your argument is a wash.
Pumpkins, for culinary use, are a side-benefit to many people who buy them for fall decorating (not just Halloweeen, you understand) and then, rather than waste them, use them for eating. True, jack-o-lantern type pumpkins are not the best for culinary purposes. But why waste food at all if you don't have to? Here, again, processing is required by the user.