Brandon over at Siris has (had, for I am slow) a post about a number of things, but the one closest to my heart is the rough treatment Xenophon receives. I think the reasons he gives are accurate, but not complete. I think that one major reason Xenophon is disparaged as Plato is praised is that Xenophon's Socrates is much more human--and that he dies a more human death, for a more human reason.
Preface: I wish I had my books. This is from hazy memory. But Xenophon's Socrates is very far from a Platonist. He goes so far as to claim that nothing is "good", but that things are only good for something. And in his death he remains far from the unyieldingly philosophic, truth-seeking Socrates of the Phaedo.
In the Phaedo, we see an unrepentant Socrates declaring that the philosopher is constantly practising death, and so should not fear it when it comes. He has chosen to die rather than to cease his eternal questioning, and his last words, "Crito, we must sacrifice a cock to Asclepius; see to it, and do not forget," are positively heroic. I will here admit that I get choked up every time I read it, and indeed whenever I think about it.*
This is the philosopher at his best, facing death, unafraid and cheerful and resolute. And I think the myth has especial resonance for lovers of philosophy, since so few philosopher were anything like heroic in this same manner. Who else in the history of philosophy dies this way? To whom shall we look for another such example of living the philosophic life? Whether from lack of need or opportunity (charitably), or courage or conviction (un-), no one else has made so clear a choice between such stark alternatives. When we consider the... less respectable life of a Nietzsche or a Heidegger or even a Kant, it becomes obvious just how far above these lives Socrates' was. And so philosophers, not otherwise noted for living well (however fairly or unfairly), can always point to Socrates.
Xenophon, however, rips this story away. His Socrates chooses death not because of some refusal to compromise his skeptic's integrity (although his innocence is a confort to him), but because he is old. His faculties are failing, and to avoid this he thinks it better to die than to suffer this indignation. The heroic Socrates of the Phaedo is replaced with the merely human Socrates of the Memorabilia, and the only really philosophic death among the great philosophers is replaces with an early form of euthanasia.