This is true -- but the rail would not present a real alternative, IMO.
Who's going to pay train fares for a ride they can make in an hour and change? As bad as traffic is, people will still use their cars for a ride that short. This isn't NYC, where a significant number of people don't own cars. Nearly everyone in Tampa and Orlando has a car already, and they're not going to give it up.
Also, if you're in Tampa trying to get to work in Orlando, your "high-speed train" is going to save about 10-20 minutes. And as meager as that is, it's actually not a true number -- because the car ride is door-to-door, but the train ride doesn't count the time getting from your home to the origin station, and the destination station to your actual destination.
Not to mention the fact that there is no real way to get around the Tampa and Orlando areas without a car anyway (none that would appeal to most people anyway -- who wants to ride a bus to work?).