Lots of people travel for conventions and never planned to go to WDW. They may go to Sea World since it's literally within walking distance, if they even have time, an interest, or could even afford it. They more likely would add a couple days to their Orlando stay and go to USO because it's right there almost and has much better appeal than Sea World. The case for USO is bolstered even further with Comcast investing billions to fix it up and add new stuff...and, oh yeah, HP.
An easy connection to WDW from I-Drive not only may convince these people to spend some of their time over in Mouse World, but may even convince these conventioneers to book on WDW property. Disney could even capitalize on this further by adding new convention facilities at or near EC.