Ashley I've seen this get asked a lot, it doesn't really affect me so much personally but I think I'm aware as to why it's popping up a lot:
If an object is twice as wide and half as tall, what's its scale?
If you have an Sprite that has an imagewidth and imageheight of [32,32], and you then use "Set Size" or "Set Height/Width" actions so that the sprite is now "64,16", then that would mean the scale is still at 1.
So continuing from the example, you're 32x32 sprite is now 64,16 via "Set Size", if you were to set Scale to 2, I think people would expect the size to go to "128,32", rather than the Scale action reading from the image data and setting its dimensions to "64,64" (which it currently would do).
This leads me to believe the way that "Set Scale" is implemented is simply doing a formula, reading from the ImageWidth/ImageHeight (and NOT the sprite.width/sprite.height), therefore "Set Scale" is more of a quick formula action, rather than a built-in variable that is storing the Scale value. If this is correct, then I think that's why people are confused at the lack of retrieving a Scale value, because you simply didn't design it that way :P
Again, workaround is easy but yes. Hope I was of use!