Yes, there is really a market for these devices
Or do you not have a laptop or PC? Both are refreshed all the time, though the more major refreshes tend to occur roughly yearly to match Intel's tick tock cadence. Do you have a TV? Most are refreshed on yearly cycles. Do you have an automobile? Most are refreshed on yearly cycles, and like iPads and iPhones, get some small refreshes on a yearly basis plus bigger refreshes a bit less often.
Just because Apple introduces a new iPad or iPhone, or Samsung introduces a new Galaxy S, doesn't mean that your older model is suddenly worthless. Those who buy these as a fashion item may want to have the latest model, but that's a rather less expensive affliction than those who insist on having the latest fashion in clothes or whom trade in their car for the newest model every two years like clockwork.
Operator subsidy, or lack of same, is also irrelevant. It would really only matter if you bought a model with cellular, which I don't see as being all that necessary for a tablet. All it does with phones is hide the true cost, which is not really all that different than how people who buy a new car every two years think (i.e., trade the old one for a new one in exchange for essentially adding two more years worth of the same payments you were already making, which means its "FREE" lol)
I don't even understand the point of your complaint. Are you saying that tablets should never be updated, so you can buy one and never need another one until it breaks, like how you buy a washing machine or a hammer? I'd prefer some technological advancement, and am willing to accept the risk that my product will become (gasp!) outdated in comparison with what else is out there over time.