Originally Posted by Wy Renegade
The ratio of surface area on filter media vs. that of natural substrate and rock is also an often debated question. In reality, most modern filter materials have significantly more surface areas for bacteria colonization than the normal substrate that is included in aquariums, which is why they are significantly more effective at nutrient export. It that wasn't the case, everyone would still be using undergravel filters, as they take advantage of the normal substrate space available for bacteria colonization. The reason we've switched to modern HOB and canister filters is because they provide more surface area for bacterial colonization than most substrates and are therefore more effective a filtration. A quick good search in regards to surface areas of ceramic filter media or even bioballs bears that out.
Every once in a while I search for some evidence to support the whole "high-tech filters are better than a sponge filter" theory but I have yet to ever find any.