Facelookbovvered - I agree with your point about the higher APD only applying if one books a through ticket. However, in most cases, the saving on the APD is usually outweighed by the increase in the other components of the overall fare. Thus, a customer is incentivised to book a through ticket for a cheaper overall price, with more of the money spent going to HMRC rather than the airline / airports en route. HMRC know this, which is why they manage to get away with this scheme. I doubt HMRC really care *where* exactly you are flying - they care only that they get their money !
ayroplain - tell your mate to print the boarding card twice, once from his computer at home, and once from the computer at the office - I believe that reprinting a boarding card yourself is free. It does however sound like a fault with a printer (or something physical related to it). You can buy a new black+white laser printer for under £50 if you have a search around the web. 2nd hand on Ebay should be rather cheaper.
I'm interested as to how your friend manages to fly so much for under £20 - assuming he has a Mon-Fri job and flies mainly at weekends. Round trips on this fare with almost any other airline are very difficult to obtain, and while I've done a few trips to Hahn for tuppence ha'penny, it's rather more difficult to achieve if visiting the southern Med in summer !
Ryanair are not renowned for getting the wording exactly right on their terms of business - improving the drafting skills of their in-house lawyers would be an idea. While technically you can hold them to it in a court, it's a pain in the b*m to do so, meaning that unless the sum involved is significant or you are *really* cross with them, it's usually not worth the hassle.