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Google might look at these pages as "doorway" pages.
I have some sites with extremely high bounce rates (80%+), but sometimes that's just the nature of the content.
This sounds like good thematic "siloing" to me - and it makes sense in a lot of ways as long as you have a good general top-level navigation for the site.
Planet13 have you determined what key terms you lost.
I would look over anchor links you built up over the course of your optimizing the site. See if there is a relation to the links and the key terms you lost.
Anyway i find that increasing interlinking between the blog and eCommerce areas actually drives improvements in the SERPS and that doesn't mean your standard drive the user to your sales page type linking.
I'd guess that the article visitors are searching for info on the topic, so they're mostly not shopping. But the articles seem like they have several things which should Google should like...
I should mention that, indeed, when appropriate, I do link from the ecom pages to the blog pages. I tend to agree with your premise; if it is good for the users, then it is good for SEO (which I think is what you are saying).
On March 23rd it was a rankings drop of about 3 to 4 spots "across the board." So it was the main keyword "blue widgets" and long tail that had widgets in it. Plus, it was words that were unrelated to widgets (or blue) at all.
I thought we were talking some major rankings problem here.