<ww:if test="#myObj.myString == 'A'"> Why doesn't this work when myString is equal to A? </ww:if>
OGNL will interpret 'A' as a char type and not a string. Simple solution - flip the double and single quotes.
<ww:if test='#myObj.myString == "A"'> This works! </ww:if>
Alternatively, you can escape the double quotes in the String:
<ww:if test="#myObj.myString == \"A\""> This works! </ww:if>