I've noticed that a transaction will not register in a receiver's wallet for about 5 minutes after being sent. In Bitcoin, it is registered immediately and then you wait for confirmations. My question is not about waiting for confirmations in order to unlock balance, but about the simple "registering" that a transfer was sent. Does anybody know why we have this delay?
Fresh transactions go into the mempool before they get mined into a block. Current version of Monero-wallet-gui (and also monero-wallet-cli) does not scan the mempool for incoming transactions, therefore the transaction needs to be included into a block first so the reciver is able to see it.
This will be different in the new Version, where monero-wallet-gui is able to scan the mempool directly, which will make transactions visible after seconds.
Transactions that are not yet included in a block are stored in the memory pool. When you submit a transaction to the network, you'll almost immediately see your transaction stored in the memory pool on a blockchain explorer, e.g. http://explore.moneroworld.com . Average block time is 2 minutes, so the newly created outputs will be unlocked roughly after 22 minutes (for 10 confirmations).