Is the bicoin: URI scheme an URL scheme as well? Hi given that bitcoin:1335STSwu9hST4vcMRppEPgENMHD2r1REK is a valid URI. Is it a valid URL (locator!) as well?

I tend to say yes when I compare sending bitcoins to a bitcoin: URI with sending mails to a mailto: URI. The latter is according to RFC 2368 an URL scheme.
I took a look this. Bitcoin doesn't reply fit any of these perfectly, but I think it is a URI in that it uniquely identifies a Bitcoin account. The issue is that Bitcoin doesn't really have a location function. I suppose you could say that you can locate Bitcoin address history, but that's not really the purpose of a bitcoin: link. I'm going to say no, it is not a URL. It is however a URN.

EDIT: mailto: is a URL the same way a HTTP URL is. It has a domain name and states the location for sending something. Given this example, I'll change my answer to yes.