Not every web site does this, but enough of them do.
Now you can protect yourself by using temporaryinbox.com
Just make up an address on the fly- xyz@temporaryinbox.com and use that to register. then go to www.temporaryinbox.com . Once there, you can retrieve your registration email, and away you go. Whatever address you use is then deleted from their server, and any spam is just lost.
The site works on Donations, so I you like it, send them a few bucks
The site works on Donations, so I you like it, send them a few bucks