I expect forum sponsors to be pushed a little more, after all that's what they pay their money for.
But the main reason the small brands on here get pushed more is because they're seen as people, rather than a faceless brand. People like Matt @ H4L are probably regarded by many as friends/associates, and you're always going to recommend them over a faceless brand. You'll also be more forgiving and won't say as much negative.
Other brands such as Aldred or Blenheim who don't engage struggled, and aren't pushed to anywhere near the degree of those that do.
I like to see brands contribute, rather than just pay the £15 a month - and I think if more did that then it would work to the benefit of both the forum, the brand and the members.
I agree in part, they pay their money for the platform in which to operate.
If they think buying the space means they are going to sell stock then they'd be a little wide of the mark.
The bit i totally agree with is that you need to contribute, market yourself! You have the platform so use it... Each small business has a genuine personality. They have to and will because of the way the come about... allow that through and you build up character and a relationship with your audience. Forget the buzz words, advertising proper and alike... be yourself like an old shopkeeper and you'll get better interaction. The more this happens then your name becomes vocab for that audience and an option for a sale.
Lots can be done, just be realistic... as everyone fights for that tiny % of market share. Ask yourself are you doing more than the next guy to gain it?
Plus the more interaction the more people can really learn.