not sure yet how this is relevant, but it is backed by people i trust with webarch
The idea behind URI templates is blindingly simple. There are lots of conventions that people use to denote the variable parts of URIs; one of them is to use {brackets}. All that we’ve done is codify that practice (brackets are a good choice because they’re not allowed in URIs, so there isn’t much risk of collision).
2007-07-28: hopefully leading to more REST hygiene in internet systems