Well, that's kind of how we do it now. But while it works better than truly parsed, flat HTML, it isn't as practical as you'd think.
Like I said, we have a couple dozen sites. Some have hundreds of pages of content. The editors, as is their wont, often want to change the layout or whatever. As there are several sections of a site, it become a HUGE pain to make changes, even with includes.
In addition, because we are so short staffed, we would like the editors to be able to write and post their own copy rather than send docs to the web team to HTML-ize. But, we don't trust them enough to give them a full HTML page to edit, because some table cell will invariably get out of whack and then we have to fix the damage. It sounds harsh, but it's true.
So--we want to use a template system. We create a template that is the wrap. Inside goes the actual content. So the contact_us.html file is really only a some text with basic css markup. The editors can futz with this to their heart's content, with no chance of mucking up the page.
Also, at the drop of a hat, we can completely change the website look and feel with a simple template change. That's powerful stuff, and I hope you see the advantage over having to touch every page, even those with includes, because if the design changes in some fundamental way, the includes can become irrelevant.
Anyway, the challenge is getting Dreamweaver (or some other editor... GoLive?) to work in this environment--seeing the copy within the wrap, with the styles applied, but not editing the wrap. If anyone has any advice in this area, please let me know.