Nitpick but isn't it the other way around:

% gem install rcov
Fetching: rcov-1.0.0.gem (100%)
Building native extensions.  This could take a while...
ERROR:  Error installing rcov:
        ERROR: Failed to build gem native extension.

        /usr/bin/ruby1.9 extconf.rb
**** Ruby 1.9 is not supported. Please switch to simplecov ****


versus:

admin:~ # gem install -r rcov
Building native extensions.  This could take a while...
Successfully installed rcov-1.0.0
1 gem installed
Installing ri documentation for rcov-1.0.0...
Installing RDoc documentation for rcov-1.0.0...
admin:~ # ruby --version
ruby 1.8.7 (2011-12-28 patchlevel 357) [x86_64-linux]