Airs do go into standby mode more readily than other macs.
Assuming its not just the extra time to exit standby mode (and isn't really sleeping anymore), have you checked the startup disk preference as the article above recommends?
You may have to look in the console log for sleep / standby messages in case your mac is entering standby / hibernate earlier than the expected one hour. The
pmset command can show you the details of your Air's power management settings. Here's what a Mid 2011 Air looks like with mostly default settings:
mac:~ me$ pmset -g
Battery Power -1
AC Power -1*
Currently in use:
You can also use
pmset to change either the number of seconds before standby kicks in, which is
standbydelay; or turn standby off completely by setting
0. Use the command
man pmset for details.