You are correct that this is currently not natively supported in Android, although Google has been saying it will be coming ever since Android was officially launched.
While not natively supported, the hardware on every android device released to date do support it. It is just disabled in software, and you would need to enable it in order to use these features.
It is however, fairly easy to do this, but you need to be root, and the specifics may be slightly different between different devices. Your best source for more informationa about this, would be XDA developers: http://forum.xda-developers.com/forumdisplay.php?f=564.
Most of the existing solutions are based on replacing wpa_supplicant, and is the method I would recommend if possible on your device. For more details, see http://szym.net/2010/12/adhoc-wifi-in-android/.
Update: Its been a few years now, and whenever I need an ad hoc network connection on my phone I use CyanogenMod. It gives you both programmatic and scripted access to these functions, and the ability to create ad hoc (ibss) networks in the WiFi settings menu.