Management and clients have to take a very conservative approach to languages, because they have other problems than you have as a programmer. Ruby is an exquisitely powerful language, yes; but the manager and client also have to worry about finding somebody who can maintain Ruby stuff after you've gone on to other projects, and worry about whether Ruby will change so much over time that it'll end up being high-maintenance, and so on. Perl and Python have had the time it takes to establish they're safe about these things. Ruby hasn't, yet.
In 5 years, you'll have their wholehearted support to write in Ruby and you'll be miserable because something even better will be available that they're nervous about using.