Why are KS1 results scaled up?

[wrinkleseverywhere]

DC1 is just finished Yr2. I got her SAT scores this week and, not knowing what they meant, did some googling and found out about the raw score, scaling up etc. What are the benefits of having it go up to 115 with expected being 100? Why couldn't it have been left as being out of 40 (for example) with expected as X? Does it tie into something else?
I'm just curious - and confused!

It is so they can change the boundaries each year depending on results but keep the scaled scores for year-on-year comparison.

Most schools don't give out the scores, raw or scaled. Just the judgement of Towards, Expected or Greater Depth, based on the actual tests plus teacher assessment of the year's work.

Thanks for replying. I think that that makes sense.
One more question if I may - what is the difference between Greater Depth & Exceeding? Actually, what do either of them mean?