Yes and No
Firstly I think the government was of the mind set that most responsible classic car owners who take pride in there car or cars would obviously make sure there car was road legal.
A high amount of classic car owners make there cars better then New and far better than when they left the factory floor.
Lets not forget a MOT certificate is only as good to the day it was issued / hour it was issued on any car modern or old it is for the driver of any vehicle to make sure it is legal and road worthy MOT exempt or not.
Just because a car is Mot exempt does NOT mean you can ride around with a get out of jail free card.
Of course there there will always be a dodgy Dave trying to sell you a wreck of a classic that he doesn't want to MOT
But like you and others you have identified that problem and avoided them, You have used whats called common sense something lacking in the UK.
The amount of classic car owner who enjoy keeping to the rules of keeping there car 100% Road legal and serviced far out weights the odd
dodgy Dave's of this world.
And I can not think why everyone who keeps there car legal should suffer an MOT some classic cars are only driven 1 month of the year with owners making them better than new and all the costs that go with the ownership.
Some MOT inspectors just don't understand classic cars with play in the steering wheel that comes as standard.
I once failed at one garage and went to another and got a pass it is up to the MOT inspectors brain at the time.
Why don't you MOT the car yourself take a Jack and and something to lay on and a inspection torch jack it up and have a look around take all the time you need don't rush.
Just because seller doesn't want to put a MOT on the vehicle it doesn't mean its a shed he could be busy but be a genuine seller.
Dont forget there are messers out there they call you up hello mate have you got the car for sale, Yes, Can you Mot it of course I can
then buyer no where to be sean.
If the seller is not happy you turning up with your jack and spending as much time as you need to understand what the car wants ?needs
ect then I would abandon the sale. and if it is miles away and your buying it blind I would also avoid it.
I wish you good luck