Well, not exactly.
Infocom wrote their languages in a proprietary language called ZIL
(if I remember correctly). ZIL didn't compile into native code, but
into something called Z code that's executed by a "virtual machine"
called the Z machine. When Infocom wanted to release their games for a
new platform, all they had to do was to write a Z-code interpreter for
that platform.
What Graham did was to design a totally new language, Inform, with
a compiler that compiles it into Z code. The output of Graham's
Inform compiler has the same format as that of Infocom's ZIL compiler.
The fact that most games written in Inform are so similar to Infocom's
games is a concious design decision, both by the games' authors and by
Graham, when he wrote the Inform libraries. But there are at least
two games written in Inform that are *quite* different: if you haven't
tried them yet, check out "robots" and "freefall".
Magnus