I'm recently made a WP + XF website. The site has 2 weeks since it went live. However, I'm seeing that Google indexed the front (Wordpress) very fast and easy and the forum has only 2 pages indexed..after 2 weeks. I've added the site to Webmaster Tools...tested if Google Bot has some problems crawling..added a robots.txt file etc...all is in order. However, Google is still not indexing the forums section of the website. I'm now looking for a sitemap generator for XF (haven't been lucky so far) but this is my last idea.
I have no proof of this, but my gut feeling is that google assigns various weights to the type of software formats.
A forum which is not very busy and not well linked both in and out...and has not been up for a long time...is not likely to be indexed well. But a WP installation can be!
Some of this make sense. Most WP installations contain blog posts, news stories, articles and other more stable and long-lasting content, while forums move quickly. So goog may have some "weightings" on these.
I am going to watch this long-term with my new drone site! One way I am working it is this. Each full article or blog post in the WP has a continuation thread in the forums. So, right away, each good article links both in and out of the forum.
My forum is also brand new, while I took over an abandoned WP blog. So there was at least a bit of mojo in the WP installation, but zero in the forum.