Maybe they are using the publicly available information for their survey as many airports have them available on line?
Very likely so, but you would have to ask how many airlines actually pay them! I guess if you landed at BHX, say as a diversion, without any rate agreement in place you would, but any carriers looking to give the airport regular income / revenue they'd be looking for a much better deal. I imagine that BHX perhaps doesn't necessarily want to attract one-offs, so prices itself accordingly.
If an airline believes there is money to be made flying a route, they'll have done their sums based on all the operating costs, which will include landing and handling fees, and what must surely be the biggest slice of all - fuel. The landing fees will be a comparatively small proportion of the overall cost - important but not the overriding consideration.
Final thought, if BHX is really so expensive, how come so many ad hoc freighters find it an attractive arrival airport?