Madmatt,
Good comments Matt. Here is why they are made like they are. A solenoid would cost more than the actuator plus the wiring and switch is more complex and expensive. The vacuum requires really inexpensive tubing and is simple to hook up and easy to adapt to anything. The 4" actuator lets cars with as low as about 10 inches of vacuum at idle easily build up enough vacuum in the reservoir to pull and hold them open. The spring that holds them shut has some force but the 4" actuator has enough "guts" to yank them open.
Tom Hand