Right, it does seem poor considering the number of people who want to take a day away from the mouse and try Universal.
Disney tolerates the Lynx buses that run from the TTC to SWF, but I don't think they'd let Universal buses on property. Getting from Disney to Universal by Lynx would take 2 hours with 3 different buses, no one has done it. But they have gone to SWF and that works just fine taking the #50 from the TTC.
Universal has shuttle buses that travel from the onsite hotels to WnW and SWF, but not Disney.
Nope, the mouse doesn't want people leaving the property. They want people to stay the entire time like nothing else is there. That's why Disney started the magical express thing taking people from the airport to their hotel for free.
Even though you said you don't want to rent a car, that's the best answer. It may cost more, but the convenience factor makes up for it. Otherwise hire the limo. When staying offsite, you want to arrive early, like at 08:15am and be at the front of the gate.
Mears is probably the cheapest, and they've got an "in" with Disney. The phones in the lobby have a direct way to call Mears. The only downside with them, is they pick up others along the way. So if you hire Mears, go for a 7am leave time. Early, Early, Early is the key.