"In reality, the different types of SSL/TLS certificates all serve a single purpose and that is to encrypt the communication between a browser and web site. Anything extra is seen by many as just a marketing gimmick to charge customers for a more expensive "trustworthy" certificate."
NO!!! If if the "single purpose" was encryption, browsers wouldn't throw a hissifit when a site uses a self-signed cert.
CA-signed certificates are just as much about Identity The CA is vouching that the key in the cert does indeed belong to the entity that controls the domain
EV certs go beyond that to verify that the the key in the Cert belongs to the legal entity claimed in it. Just because normal users don't understand it, doesn't mean that it has no usefulness. Do you think users would give a crap if browsers didn't go into Red Alert whenever you tried to type a password on a non-SSL site or browsing into an self-signed HTTPS site?