1script - 10:05 pm on Feb 2, 2013 (gmt 0)
This may simply be a technical issue - most forum platforms, at least in their default installed form, are and have always been terrible as far as even the basic SEO is concerned - no canonical URLs, session IDs in URLs, both threads and individual messages indexable (and sometimes under a few different URLs each), various sorting representations of the same content indexable under different URLs and the list goes on. Name a particular glaring technical SEO issue - all forum software packages have it unless you spend time to find, install, often times pay for a patch that cures some of the issues. Usually, with every basic system upgrade you break all your patches and the list of SEO related issues goes on.
I see some sites creating posts just to talk about a forum thread's subject just to outrank the thread right now. Many of these link to the thread, including some to WW.
Wordpress is much cleaner from the basic technical SEO stand point out of the box and many easily installed SEO-oriented plugins exist, so any site starting out as a WP blog, has a head start compared to a forum site just starting out with all defaults.
I would say that having a prominently featured blog with anything other than site update notices in it, one which emphasizes the point of view of the forum site owner, may be detrimental to the free flow of opinions and therefore the amount of discussions and UGC thus created. Some people would feel pressured to comply with the "official" point of view of the site and leave to find another one instead.
Personally, I've tried many times to either grow a forum at a blog site or add a blog to what was originally a forum and had succeeded in neither.
I would be very much interested myself in how this particular discussion turns out and I might suggest extending it somewhat by adding thoughts on what else, other than, or perhaps together with, a blog can be added to a forum site to supplement without jeopardizing its main sources of referral traffic. How about a directory, for example?