Though why are Ryanair allowed to get away with such scandalous treatment of its passengers?

Er, they weren't allowed, hence the fine. I know that authorities in both the UK and Ireland were planning similar action until Ryanair capitulated and agreed to abide by the law.

Something to be aware of when buying airline tickets that Ryanair et al do is try and sell two single tickets, as it greatly reduces their responsibilities on the return leg of any trip.

Yes but if your return flight, albeit on a single ticket is delayed they are still liable to either offer a refund or a journey on another date.

Yes, but they can avoid a lot of the lodging and sustenance requirements that would have been present with a return ticket I believe.

I can see why if they are on an outward bound trip but that really should not apply on a return case.