I check every plane. They're VERY different in terms of comfort.
Maybe if you fly US domestic it doesn't matter. But for international flights aircraft type makes all the difference. (see e.g. Emirates horrible 777 vs it's very comfy A380)
I check as well. However, the airline can/will change the aircraft at their discretion. Last time I didn't find out until I arrived at the gate. If you don't want to fly on the changed aircraft, I'm not sure what recourse you have at that point. Of course, ultimately you can not board, but there may be penalties.
If you had carry-on only, it might not bother them much. If you checked baggage, they need remove it, causing a delay. Although in principle, this would be "just as if" you missed the boarding call, I suspect if you tell them ahead of time (as in: "I'm not boarding this plane."), they'll try to persuade you there will be penalties. I don't know.
There must be fine-print in the contract of carriage, since the ticket ("product") purchase indicates the aircraft.
Perhaps one could verify the aircraft before check-in. If you don't receive a boarding pass, obviously there is no problem whatsoever, you just lose the flight unless you've paid top-dollar for a refundable ticket.
Where there's an obvious external difference it's easy to differentiate (number of engines in the case you cite). However most domestic US flights are on single aisle twins that all look alike.
You’ll probably notice a difference in comfort (especially noise) between a 737 and a320, say. And you can tell the difference between a 737 and 757 by the way the 757 is unreasonably long (see also, a321).
