I don't use the car dock, mine only comes up with the slide for answering a call on the first call after a reboot.
You can of course use a headset, then it wouldn't matter, you just hit the button on the headset to answer.
So what does yours do after the rest of the calls after the first initial slide??
Mine actually just did the opposite.. i had rebooted my phone this morning, got a call and it was the "push to answer/ignore" option like in the car dock.. then the second call was slide....
Headset is only useful if i'm driving.. i'm saying i would like mine to be push to answer always even when i'm NOT driving.