[Jeph]

Some one correct me if I'm wrong, but this is a throw-back to the ol' racing days. Similar to why Posrche has the key on the left side (which is where the button is supposed to go -like the S2K), it's for racing. It's quicker/easier than turing a key, and being on the left side (on a left side drive car of course) allows the opposite hand to be on the stick.

I wanna say the Honda S2000 brought this back. The Viper SRT10 has it, but it's on the wrong side. Then luxury cars such as BMW, Lexus, & Mercedes made it a convenience feature -key need not be inserted to start the vehicle. It's pretty cool on some Mercedes, where the button is on top of the gear selector.

On some cars it's a throwback, others it's convenient feature.