Hello!

I'm new to scheme and gambit. I've read "A tour of scheme in Gambit", and now I'm learning the language through "The scheme programming language" (http://www.scheme.com/tspl3/).
My question concerns define-syntax VS define-macro.
If I understood well, the first is standard scheme (*) whereas the latter is not. Besides, "A tour of scheme in Gambit" qualifies define-macro as "unhygienic" (**). Moreover (as I am from Haskell), I find define-syntax's pattern-matching simpler. So:
1) What is the point of define-macro? Why does "A tour of Scheme in Gambit" encourages to use it, since it doesn't detail define-syntax?
2) Why does gambit run by default in a non-standard mode (Gambit scheme, gsc -:S) in which define-syntax doesn't exist whereas it is standard?
3) I plan to use termite, which uses Gambit Scheme and not standard scheme (gsc -:s). Can gambit scheme code call to procedures written in standard scheme?

Thanks!

(*) By 'standard' I mean R5RS.
(**) Word which, from my newbie point of view, kind of sounds like "evil" or "don't-you-touch-it".