Well, you cannot compare sites like this, just basing your analysis on the script used.
Many other criteria are involved, like the size and age of the site as well as the success already reached.
Comparing a site with few thousand pages with one with hundred of thousand does not mean much.
Generally speaking, benchmarking an SEO technique is very hard, because we are dealing with parameters that are altered by the experiment, just like in quantum physics.
Ideally, an attempts to benchmark an seo technique would consist into starting two websites only being different by the SEO technique we'd like to benchmark, but in this case also, the experiment will be altered by the fact the two suite would most likely be penalized for duplicate content, since the content should be the same for the comparison to mean something precise about the SEO technique tested.
When implementing a new SEO technique on an existing site, it makes a bit more sens to try to see if things are better after done. But even in this case, many criteria will be involved.
For example, if the site was constantly loosing visitors for month before you implemented the technique, SE could need more time to be teased by it than if the site was already growing well before.
And, all this still depends on the quality of your content, a site with barely no content or with very poor content will probably not win anything by implementing SEO techniques.
This being said, it's very far from meaning that SEO techniques do not have a positive impact, when some SEO techniques are implemented on a good site, the impact will be significant, nothing predictable like you'll be first in SERP on all queries, but overall, there will be a measurable boost.
You'll find many testimonials of this here on phpBB SEO.
Then, to conclude, the vb site you are comparing yours too seems to obtain better results because it's a bigger and better known site than yours. But this does not mean that the vb site would not obtain even better results with SEO.
Recently I posted about a similar matter on phpBB.com : http://www.phpbb.com/community/viewtopi ... 5#p6703645
phpBB.com is typically an authority website, chances are great that if you reproduce your experiment there, you'll obtain the same result, but, as you can see from my post, results could be a lot better, phpBB.com is actually very far from being fully crawled.