but maybe that's simply because the perl script claims the 'inactive' memory that these other programs had been using.

Indeed. It is that exact scenario that my brother experienced that brought this to my attention.

He'd just installed a new piece of software that used a substantial amount of memory, and he noticed that all his other regular programs seemed less responsive. He thought he'd acquired a virus :)

Once we worked out that it was just that those other programs were no longer benefiting from having much of their runtime state preserved in 'inactive memory' whilst the new program was running, he praised rather than cursed the feature and was happy.