Due to floating point numbers imprecision, 90 isnt always going to exactly equal 90 when converted into a float.
If you are having trouble comparing them you can use Mathf.Approximately(a, b) to compare them to see if they are ALMOST the same.
answered Jul 19 '10 at 11:31 AM
When you type into the inspector, it changes a quaternion internally via the euler angles you provide
That means that your three numbers get turned into a 4 number object, and then when they're read back, it's giving you as accurate as a float can represent for the object
Basically: it is 90, but float precision isn't accurate enough to keep it exactly there, so you shouldn't worry about it - you'll never notice it
answered Jul 19 '10 at 11:28 AM