There seems to be an assumption on the part of all universities that are prepared to give a year out to sick students that whatever condition the student is suffering from it will be sure to have abated substantially or gone away in a year's time.
In the case of ME it's quite likely that the illness won't have gone away in a year's time, or even abated, so I don't see the point of offering students with ME a time-limited leave of absence. But this is what all universities almost invariably do.
I've mentioned elsewhere that schools and employers have the same narrow view of the way illnesses play out, and expect that if they offer someone what they see as an ample six months or a year off, that person is bound to be ready to return to school or work by then, and if he or she is not, then the obstacle is unlikely to be physical ill health, but something psychological - the thinking being that generally only psychological illnesses take longer than this to resolve.
The reason universities grant extended leave to sick students is presumably to enable them to return and complete their degrees when they are well enough to do so. In the case of ME - a chronic and debilitating illness for which there is no cure and the symptoms of which are exacerbated by any kind of stress - the leave that is granted and the conditions under which students are required to resume their course should be specially tailored to the nature of the illness; that means offering indefinite leave and very accommodating conditions of return.
Oxford colleges may well pride themselves on their academic rigour, but they're clearly not very enlightened about the nature of one fairly common medical condition. Dominus Illuminatio Mea, their motto says, and it looks like the Lord, or someone, could do with shedding a bit more of his light on them.