The questions Schiavo’s guardians must answer are, What benefit will she gain, and what burdens is she being subjected to, in being kept alive in her condition? Is the preservation of the life of someone in a permanent vegetative state actually a benefit to that person? Is it a just allocation of limited resources? Traditionally, Catholicism has answered no.
Without getting into the particulars of this case, it is absurd to state that Catholicism has traditionally said the preservation of the life of someone in a permanent vegetative state is not actually a benefit to that person and is an unjust allocation of limited resources.
The medical technology to preserve the life of someone in a permanent vegetative state is about fifty years old. I assume the medical definition of permanent vegetative state is no older, since before feeding tubes people didn't survive three months in a persistent vegetative state.
The questions the Commonweal editors say must be answered would have been meaningless to anyone fifty years ago, so whatever traditional answer Catholicism has doesn't have a very long tradition behind it. (Commonweal itself is fifty percent older than feeding tube technology.)
It's true that a lot of people claim the tradition (back to the Sixteenth Century at least) supports an answer of "No." A lot of other people claim it supports an answer of "Yes." The bishops say the answer is not yet clear. Any way you look at it, though, new medical technology demands a development in Catholic health care tradition, not a rote application of the state of the tradition c. 1950 (or 1590, or 1270).