Negate the need for blockchain explores and full blockchain syncing for simple queries
That's exactly what your bitcoind client does. It asks for specific blocks in network calls and if you wanted to, you can create a simple client that asks only for certain tx's and blocks like you said.

That is in fact what most SPV wallets (phone-based wallets and some others) are doing. They ask for block headers only and then ask for transactions related to those blocks to prove that certain transactions exist.