"Brute force" methods rely mostly on trying every possible combo of letters and numbers, so it shouldn't matter what method was used to generate the password in the first place. Any possible 64 character password generated by that website could also be generated by other means, including monkeys randomly hitting keys.
The overall security of a password relies on more than just it's length and randomness. It also relies on the method used to input a password, and the relative value of time vs reward, especially when it comes to brute-force methods. For example a system that becomes inactive after X number of incorrect entries can greatly affect brute-force methods.
For GW, most of the account hacking involves key loggers, fake websites, or other methods of capturing the actual password and/or, in some cases, simply guessing the password when someone uses simple passwords like their girlfriends name or whatever. Trying to brute force a 64 character password for GW would be impractical given the time involved and possible rewards. Even a 6 or 8 character (random-ish) password should be enough for GW.