There are also examples of sucessful tech companies with little to no marketing department (Craigslist to use an old example). I don't think he same can be said of the reverse.
"... it's clear that plenty of engineers play a marketing role in addition to their role of 'shipping'."
That is an interesting statement to make. Some really great marketers that I've met started with a CS or EE degree, and some really great engineers I've met started with Economics or physics degrees. It isn't the degree that defines them, it is where (and how) they add value to the goals of the company.
In the 'way back' times there was a video format war, it was called 'betamax' vs 'vhs'. Betamax was a better engineered standard, VHS was a better marketed standard. Then there was the "OSI" vs "TCP/IP" network wars, OSI was heavily marketed, but TCP/IP was better engineered . Word vs WordPerfect, Lotus 123 vs Excel, Firewire vs USB, the road is littered with "products" and "standards" where either good marketing or good engineering determined their success or not in the market place.
Generally it seems that if you have two competitors with equivalent engineering teams, bet on the one with the better marketing. If you have two teams with equivalent marketing bet on the better engineering team. Either marketing or engineering can cover for some weakness in the other team, so yes, I value them equally.
That you don't suggests you haven't experienced really great marketing. There was a great post by Joe Kraus (Google Ventures) on this . Something to think about.
 Some (many?) would argue that OSI was over-engineered, but either way it was heavily marketed.