I know the first two were at Willow Springs, I'm not sure about the rest.
From my experience, and the experience of fellow bikers that I know, the learning curve for riding a bike is much steeper. The power to weight ratio is astronomical compared to nearly any road car, and the contact patch is tiny. Plus you have to deal with leaning and front/rear braking. Sport bikes are like cars with 800hp and twitchy. You can lose the back end in a flash anytime, and you can't slide unless you're godly.
The bike generally is better at at accelerating. For example, most sportbikes will do 0-100mph-0 faster than a 911 will do 0-100mph.
Cars almost always have a better top end and braking.
Once downforce is introduced, bikes are toast.
Edit: Here's a link to the EVO test:
http://www.radicalextremesportscars.com/media/trackdaycar03/index.php
and laptimes:
LAP TIMES
Jaguar Palmer JP1 67.70sec
Radical SR3 Supersport 68.20sec
Radical SR3-LM Tracksport 72.10sec
Caterham R400 75.20sec
AS One 76.55sec
Honda CBR600RR 76.70sec (only a 600cc bike, which is lowest for common sport bikes)
Noble M12 GTO 3 78.50sec
Blink Motorsport Elise 78.50sec
Ariel Atom R 78.90sec
Revival Motorsport D-Type 79.20sec
Porsche 911 Turbo (450bhp pack) 79.50sec
Lotus Elise 135R 81.30sec
Vauxhall VX220 Turbo 81.50sec
Caterham Academy 82.00sec
Subaru Impreza STi PPP 82.80sec
Renault Clio Cup 86.95sec
Another EVO Car vs Bike test:
http://www.radicalsportscars.com/media/fastfeud/index.php
LAP TIMES
Crescent Suzuki GSX-R1000 1 min 5.4sec
Radical SR3 Tracksport 1 min 5.6sec
Suzuki GSX-R1000 1min 9.0sec
Porsche GT3 1min 10.9sec
Lamborghini Murcielago 1min 11.5sec
BMW M3 CSL 1min 12.0sec