If you're only ever installing one Perl program on user machines, you're right. It's a hassle to install Perl on each machine.

As soon as you install a second program, the time spent installing Perl initially becomes a better investment.

It's the same case as Java. If it weren't installed by default with web browsers, people would have to go to some trouble to install appropriate JVMs. (I've gone through that with the official Sun JVM on Windows, and it's not as easy as just clicking 'OK' once or twice.)

Java does something right, sorta, with JAR files bundling up all of the class files (and additional libraries).

Of course, some enterprising hacker might use the CPAN module to create a nice bundler with Archive::Tar and maybe MD5 signatures. Windows folks will have to get by with PPM or whatever the Indigo folks provide. I'd like to see that, personally.

The bottom line is, if you're going to give people more than one Perl program to run, the executable method isn't as nice anymore. (And once you've talked people into running one Perl program, they'll want another.)