I've got a page set as my static front page and another page (/blog/) set for my posts page (the one that triggers is_home()).
But, when I put a Section Widget in and want it to appear on all blog pages, I can't. On the Special Pages tab I select "All posts" and "All category archive pages", and on the Pages tab I select the "Blog" page. But while the widget does appear on single post pages and category archives, it doesn't appear on /blog/ itself.
I've run basic tests and it seem that is_home() returns true on /blog/, but oddly is_page('blog') returns false!
I'm not sure about the is_page() issue - but maybe the Section Widget should have an option under Special Pages for the Home/Posts page as well as Front Page?