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.