Are any hashes (Tx or block) actually stored in the blockchain? ...or is each client responsible for storing hashes for blocks and transactions in their own database? So when I send a transaction, I indicate the prev_out by its hash, and I just assume everyone on the network will know what that hash means, even though it's not specifically, literally IN the blockchain?

Is blockexplorer.com doing me a favor by listing the hash for this raw Tx? Or is that hash actually sent by the original transaction-sender?
http://blockexplorer.com/rawtx/85dce726e04af12eaaa716d00c753e2b7d6eb83a04c2c20e1b71a63d9512f03a
No. Hashes are computed upon receipt of the Tx message, and stored in a database outside the blockchain by the client/node.

http://www.reddit.com/r/Bitcoin/comments/1sqa1q/techincal_do_transaction_messages_between_nodes/