Rich, I have a cable modem, and it's always much faster than the best dialup, usually by a factor of 10 or so. So, while I've heard how with DSL you are 'separately switched' and with cable, you're on shared bandwidth, that hasn't affected me in my area. I've had it for 6 years, and it's actually gotten better over time. Not everyone is disillusioned with cable.
I work for a technology company with approx. 150 outside sales reps across the country, and all have broadband of some type. I've heard far more stories of frustration with poor DSL quality, bankrupting of companies, etc... from friends who have had both. That said, you can in fact get a fast connection speed on some cable systems.
As for installation at the Disney properties, I think personally that this is more a strategic move than anything. e.g. if you can surf the web easily, maybe you won't go out and spend as much money at the parks, restaurants, stores.
The technologies for hotel type setup have been around for years now, and plain networking gear for even longer. My guess is, its just business. Disney already has gigabit Ethernet strung throughout every inch of Magic Kindom, delivering music to individually addressable speaker/amplifier combos in trees, under rocks, etc, so they sure know how to do it of they want to. My guess is, some Disney bean counter ran the numbers, and figured you're worth more at their venues than in your room surfing.
Last, get out there and have fun, you're at Disney after all!!!