The current version of Ruby in natty is 1.9.2 p0. The current version is p290, which is the second release after p0. So if Ruby used normal versioning it would be 1.9.2.3 (or really, 2.2.3, but let's not get into that).
Anyway -- is it likely that later ruby releases will make their way into natty?
The ruby package in ubuntu depends on the debian one. And usually it's not the last one.
You can search for the rubys PPAs in launchpad and see if someone has packaged the last versions
Sorry, the version of Ruby in natty is 1.8 (1.8.7.302-2). See http://packages.ubuntu.com/natty/ruby1.8
The same goes for Debian. http://packages.debian.org/search?keywords=ruby
There is likely no way that the maintainers do a major (or minor) update in their current versions. All you get from Debian or Canonical are security fixes for the current version which do not change the version number.