I'm sure you're a veritable expert at tying your shoes in "objective" terms. What matters is how much better/worse at it you are than everyone else.
Percentiles and percentile graphs don't show how much better at something you are, they show you how many people you're better than.
For the people in the middle of might not mean much, but when people are using this to prove that smart people aren't actually smart, the difference between "I'm 1 percentile smarter than you" and "I'm 30 points smarter than you" matters.
More to the point of the test: obviously you will most likely have a lower score in the "medium term memory" portion than the "short term memory." Just about everyone would. So measuring those two on the same scale would actually make the test less useful.
That's fine, but that format of graphing things doesn't really jive well with me. Usually I associate the polygon graphs with something like these RPG stats -
And the purpose is to compare my stats against my other stats. If I'm a dumb orc, my intelligence will be very low and I just have to accept that I'll have an obvious deficiency in my skills. I don't get a correction to INT to make me feel better just because I'm expected to be bad at it in the first place and I've exceeded my abysmal expectations, I take the bad stat and instead benefit from an oddly large value in the strength department.
For the purposes of comparing myself to other people, I think this kind of graph is more useful:
Shows you where the average is, where Q1 and Q3 are (where 50% of the population is), and the maximum and minimum are (so you know objectively how close you are to the edge if you're not in the middle 50%). Just add a star somewhere to show where you specifically fall.
If the scales are different because the tests and skills are different, that will get represented by the position and size of the boxes changing. You're more able to compare yourself against the herd and you don't need to create the weird situation where some people will have better medium term memory scores than short term memory scores, but in reality their short term memory is still better.
It also kind of shows you which traits its noteworthy to be good in. Using the image above as an example, look at Series 2 Physics. The top 25% got practically the same score, so it really doesn't matter if you're the 75th percentile or the 99th percentile there. There's more variation in the bottom 25% however, so getting the 0th percentile is noticeably worse than 25th percentile.