%package -n npm-default
Summary:        Default version of npm
Group:          Development/Languages/NodeJS
Requires:       nodejs-default
Requires:       npm%{default_node_ver}
Provides:       npm = %default_node_ver
Obsoletes:      nodejs-default < 4.1

That looks very weird - i.e.: we build nodejs-default version 4.1 in this very package. npm-default declares a nodejs-default dependency, but at the same time also claims it obsolete nodejs-default < 4.1.

That sounds rather like you meant a Requires nodejs-default >= 4.1 ? then that nodejs-default version would in any case obsolete the old version of itself