Take anything and attach the word "Boat" to it, and you can double or triple the price.
The new hot tub is working out just fine. But it is taller than the old Softub, so it is harder for those short in stature to climb in. Mark isn't all that happy. So he looked online for a hot tub step. They sell them, of course, from the hot tub dealer or manufacturer for $125. Softub+ sells one, for example, for nearly a thousand dollars. Others sell them for a little less. Mark found one generic hot tub step on the Walmart website for about $90.
I said to him, "Well, what about one of those Rubbermaid step stools? You know, the kind made of plastic with a non-slip rubber insert?" Well sure enough, they have them, for like $20 or less. If you want to get fancy, you can pay $30 for this two-step job. Hint to the Rubbermaid people: Call this a "hot tub step" or "boat step" and charge $200 for it.
When we had Ginger, our greyhound, we had to elevate her dog dishes as she was, well, elevated. They sell special dog dish platforms for $100 apiece in the pet catalogs, or you can go to Walmart and buy a plant stand for $10 that does the same thing.
Capitalism is all about charging what the market will bear. And people pay for things based on perception as well as other indicia. Now, granted, if you want parts for your airplane, you aren't finding them at the hardware store - or shouldn't be, anyway. And some boat parts are very specific to boating. The stainless steel fittings for home use will rapidly rust in a marine environment. On the other hand, a plastic step-stool is a plastic step-stool.
So why the price differential? Again, when I was a youth, I was naive and thought that people made things and then tallied up their costs and added a "reasonable profit" and that was the retail price. Boy was I stupid! The actual price of things is what the market will pay. And sometimes this means people lose money selling some items (usually not for long, they go broke).
The reality is, people charge what the market will bear. And if everyone is ga-ga over SUVs, well, then you can tack on a $10,000 profit on each one, at least for a while, until someone else decides that $9,000 is an adequate profit. And of course, you can charge different people different prices, based on their own perception of value.
So a plastic step-stool may have one price for the homeowner, another for a boater, and another for a hot tub owner, and yet another for a hospital and of course, the highest price for the military (presuming it meets MIL-SPEC). A lot of hay was made a few years back about how the government was paying thousands of dollars apiece for a "stepladder" to get in and out of jet fighters. But of course, that was all political bullshit. The actual ladder was designed to attach to the plane, and wasn't what you'd find at home depot. And no, fighter pilots loaded down with gear can't hop out onto a rickety painter's ladder in a 20-knot breeze on the deck of an aircraft carrier.
This is not to say, of course, that generic products can be substituted in situations where application-specific products are needed. Not only is this a false economy, it could be dangerous. You should use new SAE bolts when installing a new clutch in your car, not the mild-steel bolts from the local lumberteria. Not only that, but it reeks of cheapness when you see someone using something like sheetrock screws to attach a trim piece on their car. It isn't worth the "savings" particularly when the dealer has those screws for a few pennies apiece.
On the other hand, there are situations where a generic product will fit in, look right, and work well. And hot tub steps might be one of those areas, provided the steps can work with slippery wet feet. Otherwise, you'll fall on your ass and end up in a world of woe....