Perl is famous for its ability to create programs that are entirely illegible to everyone but the developer who wrote them. There's a great interview with Larry on the virtues of Perl, and I recommend you read it for more info on what Perl is and what was going through Larry's mind when he started it up. I can't talk for all of Microsoft, but certainly the script technologies group and a bunch of people in the Windows and BackOffice group think it's a fine language and certainly deserves a place in Windows Scripting. I've mentioned in earlier articles that language choice is a religious issue, and Perl is a great example of this. If you are not familiar with regular expressions, think of them as the ultimate string manipulation tool for serious string processing.
Regular expressions are to strings what math is to numbers.
As a result, it's very important that we have a great Perl implementation on Windows, and that you can use Perl everywhere you can use a Microsoft scripting language. This eases some of the pain of migration to Windows, since you can at least keep using a language that is familiar to you. Pretty much anywhere is the simple answer. Windows has a technology called ActiveX Scripting that allows any script language to be plugged into any application that supports ActiveX Scripting. This was introduced way back with Internet Explorer 3.0 and is now a core feature of Windows.