There were 2 updates for Real Racing. One to get basic updates for iPhone 4 (gyro & hi-res icon, possibly some text work to make it all consistent), and another for the general graphical overhaul of textures and resolution.
The accelerometer is used if you don't have a gyro, but the gyro is a bit more accurate.
I got it and really don't see the big deal about it. It doesn't play much different than other similar games I've played on my 3G. In fact, having to move all around more is just annoying and looks dumb in public. I rather just tilt, but that's just me.