If a site can send you your password, it is not hashed. There are basically two ways this can be exploited:
Someone working at the place who has access to the password database can impersonate every single user/customer, including you, without any effort at all. So hashing passwords helps in protecting clients from some of your own staff.
If the password database is stolen, your password is immediately known, and if you use the same password on other sites, you have a problem because there won't be any time to change your password on the other sites before the thieves can access your accounts there. Password hashing can be seen as a measure to protect a user's plain text password in case of a successfull password db theft.
(You can mix and match the two exploits, too - an employee might try your password on another site, and an external password thief might only be interested in impersonating you on the site)
Hashing passwords doesn't add any security beyond making the above two exploits harder (or impossible, depending on how the passwords are hashed).
For example, to steal a password database, an attacker usually needs access to the password database, and this usually means that he has gained access to other parts of the system too; for example the database that stores your transaction history with the site, or private messages, or whatever business the site is in. Whether the passwords are hashed or not doesn't matter in that case.
Another example: An employee of the site which stores your passwords in plaintext might not even need your password in the first place. If we're talking about a system administrator, for example, he might have access to all the data you store on the site without your password, so whether it is hashed or not doesn't matter.
The use of plaintext passwords (and especially their retrieval via e-mail) might point to a lax attitude when it comes to security, which might mean there are other security problems which aren't all that visible. But there could also be valid reasons for storing the password in plaintext. There are some authentication and/or encryption protocols that require access to the plain text password.