If the webmaster of any site you visit knows the algorithm above, it becomes possible for them to mount a brute force attack on your master password from the generated password. So for this to be a viable scheme the master password would probably have to be a long string of randomness (which would probably defeat the purpose of the scheme), or the device generating the passwords would have to have a long random key that was unlocked by the master password.

Also as a practical matter the website name may not be easily determinable. Sites may have a variety of changing alternative names and addresses such that choosing a canonical string for a site may not be easy. For example are you going to refer to this site as "IT Security Stack Exchange", "Security StackExchange", "Security", "security.stackexchange.com", "www.security.stackexchange.com", or "user29349.someopenidprovider.com"...? Are you going to remember that string a year down the line, when the site has changed its address and how it presents its name a few times? An advantage of a key generator based on storage (Keepass et al) rather than deterministic generation is that at least the storage can show you what keys you've got.