The problem with such a service is that it would be centralized. That means someone controls it. That means it can be tampered with, and hacked. Imagine what would happen if everyone trusted that service and suddenly some hacker manages to change some addresses in there.
One of the main ideas of Ethereum is that you don't need to trust any entity. In reality that's not fully the case as you for example need to use some wallet created by some entity, but at least in theory you could code that also by yourself. Also, due to its nature, there is nothing "official" in Ethereum, just more or less reliable sites providing data of different quality - and then of course the blockchain itself which you can always trust.
Most reasonable services point out their contract addresses in their websites or in their github repositories and also have their contract source codes verified in Etherscan. If there is a service which doesn't publish its source code you should be quite wary of it - much of the ecosystem is based on open source principles.
