No it is not, there are/were some sites has truely instant deposit (without confirmation of the transaction). One of the site is sportsbet, they used to have instant deposit, once you sent your money then it will be credited to your account automatically without waiting for confirmation. Other site is 999dice, it has instant deposit as well. This is what I'm talking about real instant deposit (no neee to wait for the confirmation).
Disclaimer: I'm not promoting the two mentioned sites, just giving you example of instant deposit.