Autorun and Autoplay are very much related - Autoplay also uses autorun.inf to control how it acts. Microsoft seems to now call the older autorun behavior "Autoplay V1" and the new autoplay behavior "Autoplay V2".
However, it is true that removable media other than CD-ROM or DVD-ROM does act differently from CD/DVDs. CD-ROM type devices will automatically launch the program specified in autorun.inf (at least with Autoplay V1), while other media and Autoplay V2 autorun.inf files will prompt for and get user consent before performing an action.
Added into the mix is "Auto Insert Notification" (AIN), which is the term used to describe the ability for the device hardware to notify the OS that media has been inserted. AIN can be disabled for devices, but Autorun/Autoplay will still kick in in certain circumstances if you double-click on the drive in Explorer.
All of this terminology, differing behaviors for various devices, and barely documented registry settings for disabling/enabling various AutoRun/AutoPlay/AIN behaviors makes for a situation that easily confuses me.
I'm not sure what the preferable deafult behavior should be for these things, but at the minimum, CD-ROMs should behave the same as other media, and there should be a nice, single, standard control panel applet to turn the behavior on, off, or otherwise configure it.
That's my rant for the day. If anyone wants to know more details on this stuff, here's some info straight from the horse's mouth: http://msdn.microsoft.com/msdnmag/issues/01/11/autoplay/default.aspx http://msdn.com/library/en-us/shellcc/platform/shell/programmersguide/shell_basics/shell_basics_extending/autorun/autoplay_reg.asp