PIN is required for Apple Pay only if paying with a debit card, which is no different from using the physical card. Credit cards (at least our version which is chip and signature) do not require a PIN regardless of the transaction amount.
I think contactless by definition means no PIN, hence the low transaction limits that non-US customers speak of. I suppose that means it's inherently insecure because otherwise they wouldn't have these low limits.
Almost all cards here are chip and pin and, as cards get replaced, most are now contactless with a limit of £30. Apple Pay uses the same contactless terminals; if retailers have upgraded these fir Apple Pay then the £30 limit disappears but if they haven't then Apple Pay is treated like a contactless card payment which means the limit applies. Contactless cards are insecure as the moment someone gets hold of your card they can use it which is why it's only for low value transaction. Apple Pay is secure, hence no limit. Retailers here are slower to upgrade terminals because we were already using contactless; it means Apple Pay was accepted almost everywhere from day one but that in many places there's a limit.