I suspect that most of us are aware that many species do not really require a specific rod. We also know that rods branded for specific species can usually turn their hand to catching other species of similar stature.
However, I don't believe that the specific rods are not always quite as ridiculous as they sound. I know that most believe that many a barbel rod is rather handy for light carping and bream/tench fishing. Nothing wrong with that at all (and some models will be better than others), until you attempt to utilise certain tactics and they run out of steam. That's where a dedicated bream/tench rod might come into the equation. The average barbel rod is not ideal for distance fishing on huge gravel pits.
Likewise, we are scoffing at the idea of a gudgeon rod, I don't particularly disagree. However, you try to find a genuine light float rod, for all the smaller species, and your choice is going to be rather limited. Such fishing is rather neglected by the tackle trade at present.
Another thing to consider is that many a question is asked about rods for targeting specific fish with certain tactics. I know I've asked about a float rod for targeting roach before. That doesn't mean that I wanted a rod labelled as a roach rod, or that the rods suggested wouldn't be any good for other species, or utilised by me only for roach fishing.
Ultimately, many are happy with the odd rod or two that have to cover all the bases. Others believe that a greater selection of rods cover more variety of species, tactics and venues better. Rather than mock the concept of more specific rods, if you are someone that can genuinely get away with a few rods to cover all, and not have it limit your fishing in any way, be grateful. I'd love it If I could genuinely get away with a small fraction of the gear I own.