There's a bit of misinformation here, firstly, digital goods have a 14 day refund period, not 30.
"Sales are final" refers to the concept of consumer happiness - as in, "you, as a consumer, are happy to proceed and conclude this transaction"; and in doing so you void the possibility of disputing the sale because, and only because, you *changed your mind*. This is completely different from a product not being fit for purpose, which comes next:
Scirra then follow this up by stating that they are compliant with UK sales laws; which is perfectly reasonable. A business is not responsible for educating a consumer on their legal rights, and an attempt to do so may result in further complications, as accidentally misinforming someone of their rights may be construed as attempting to falsely inform them; which would be a real crime.
Given that Scirra is a game engine company and not the Citizen's Advice Bureau, I can understand why they were simply state that they comply with the relevant laws and deal with any future situations as and when they arise.
I'm unaware of the thread in questions, but the T&Cs above seem perectly in line with eCommerce laws.