Yes, you're wrong. Sort of.
Disk space might as well be free these days, so you needn't worry about that. Memory is cheap too, so you shouldn't care about being able to share memory pages between invocations of the same perl binary (if you care that much about memory you shouldn't be using perl at all).
Now for the "sort of". The only problem with shipping perl with your application is that it will only work on one platform. So I ship a script that will configure and build perl and stick it in my application's directory.