In support of other good answers, as a password cracker I'd like to add:
Password "systems" that you can remember make your passwords weaker - because if you can remember it, I can emulate it at speed.
Including the service name, or anything directly or indirectly associated with the service name, is a strategy well known to attackers - and one that we regularly exploit.
We are also well aware of (and exploit) other "clever" systems like people will use to make that service name "harder" to guess - prefix, suffix, infix, interleaving, abbreviation, repetition, reverse, duplicating the entire password, ROT13, toggling case, leet substitutions, typing letters above or below on the keyboard, typing as if using a keyboard from a different language, and many number of other transformations to make the name of the service "harder".
And even if the rest of the password is long and random, it only takes one leak from a site storing passwords badly to make all of your other passwords much more crackable.