Regarding menu icons on mobile devices, are there any official web accessibility standards for the minimum size/area of touch?
Microsoft put together some UI guidelines for designing their Windows 8 store apps. These could apply to any touch based UI.
Take a look at the section Touch, Commanding, and Controls beginning on page 65
Windows 8 User Experience Guidelines: http://msdn.microsoft.com/en-us/library/windows/apps/hh465424.aspx
Direct download: http://go.microsoft.com/fwlink/p/?linkid=258743
In particular relating to minimum sizes for touch see page 74-75
People often blame themselves for having "fat fingers." But even baby fingers are wider than most touch targets. The image on the left shows that the width of the average adult finger is about 11 millimeters (mm) wide, while a baby's is 8 mm, and some basketball players have fingers wider than 19 mm!
7x7 mm: Recommended minimum size 7x7 mm is a good minimum size if touching the wrong target can be corrected in one or two gestures or within five seconds. Padding between targets is just as important as target size.
When accuracy matters Close, delete, and other actions with severe consequences can’t afford accidental taps. Use 9x9 mm targets if touching the wrong target requires more than two gestures, five seconds, or a major context change to correct.
When it just doesn’t fit If you find yourself cramming things to fit, it’s okay to use 5x5 mm targets as long as touching the wrong target can be corrected with one gesture. Using 2 mm of padding between targets is extremely important in this case.