It becomes a scam if reasonable leeway is not allowed. For example 10 kg means < 10.5 kg. If the airline means to cut it off at exactly 10 kg they should use the proper number of significant figures in the terms: 10.0000 kg or whatever. Stating the limit as 10 kg implies rounding to the nearest kg.

Similarly for the time requirements. State "precisely 20 minutes" or "20 minutes to the second" if that's what it is. Just saying 20 minutes implies rounding to the nearest minute.

Luggage size is also a bit vague. Is the size the bag itself, or the bag plus its wheels? Different carriers treat this differently in my experience, but RyanAir's terms don't clarify which meaning they intend. To find out I had to search FlyerTalk.

In the US, when one party writes a contract any gray area is supposed to be construed to the benefit of the other party. It seems to me that RyanAir's enforcement policy does not match the most customer-favorable interpretation of its written rules. The opposite seems to be closer to the truth. I am surprised that European law would treat customers more harshly than US law, but then again I've seen in France that the customer is always wrong.