Whilst I don't necessarily agree with the tone of the 'memo' I see nothing in there that is unreasonable regarding extra fuel. It appears that Ryanair's fuel policy is the same as all three airlines that I've flown for.
If Ryanair are happy for you to carry minimum fuel then do so. If Ryanair are happy to deal with and pay for a multitude of diversions because of that then so be it.
Make sure you divert early, just to be on the safe side.