rodw, you would be surprised at the extent manufactures go to for after warranty longevity, no manufacture want the product to fail after the warranty period expires.
Being a Denso service center we get paid for information about failed parts even if they are out side a warranty period.
Think of it this way....
Case 1
You buy a new Toyota and keep it for 7 years....the vehicle is 6 years old and something major fails due to wrong material being use or poor workmanship on Toyota's behalf and you have to spend big money on getting it repaired.
Case 2
You trade in your Toyota after 7 years and shock....horror....you find you have to sell it cheap because of the know major fault with them......you loose big money as nobody will touch them....would you buy another Toyota.
Chances when it's time to buy a new/newer vehicle, you will not buy another Toyota.
BUT.....If you have no problems and get a good resale vale you will buy another Toyota.
All manufactures are very aware in "Brand Loyalty".
Bit like the Holden-Ford thing....great grandfather owned a Ford, Grandfather owned a Ford, Father owned a Ford....so what does the son buy...a Ford (even if Holden made a better car).
Remember a warranty period can last a lot longer the the statutory warranty of 3 years, every thing man made has an engineered life expediency.
Toyota have got a very very good name with reliability and I don't think they want to loose that status.