SICP doesn't 'just happen' to use Scheme; the simple language from a well-chosen combination of powerful mechanisms is the kind of thing they're teaching you to design. The medium is part of the message. (Yes, you can solve the problems using another language; I used XLisp.)
On 'dialects of Lisp': it used to be standard for very different Lisp-family languages to be called that, while nowadays someone will always contradict you if you do. It seems more of a social change than a technical one to me. (I first noticed it among Common Lispers after the AI winter.)
I know someone impressive doing real work with Scheme (though I recommended they try Lua). I don't know whether you're right about the Scheme ecosystem, as I've been elsewhere the last 15 years.
On 'dialects of Lisp': it used to be standard for very different Lisp-family languages to be called that, while nowadays someone will always contradict you if you do. It seems more of a social change than a technical one to me. (I first noticed it among Common Lispers after the AI winter.)
I know someone impressive doing real work with Scheme (though I recommended they try Lua). I don't know whether you're right about the Scheme ecosystem, as I've been elsewhere the last 15 years.