When the SNES was released in the early '90s, the concept of online play was very much in its infancy. PC gamers had dabbled with crudely beaming data over telephones in the '80s, and despite some notable attempts to replicate this on consoles — such as X-Band and Nintendo's own Satellaview service — there was never any real "online gaming" as we know it today on those systems.
Because SNES games don't have any online functions built into them, SNESoIP has to connect to the joypad port and them beam the inputs across the web to the other person's console. It's a simple yet ingenious solution for a problem that Nintendo's designers — and developers of the period — could never have predicted would exist.
Let us know if you've tried this, and share your thoughts below.