The Right to Die

I had watched the news regarding Tony Nicklinson, a man who suffers from Locked-In Syndrome and wants to end his life, earlier on today. Seeing his reaction to his case being rejected was heart-breaking: http://uk.news.yahoo.com/locked-in-man-tony-nicklinson-breaks-down-as-he-loses-aided-death-bid.html

It's ok to put an animal down when it's suffering, but why won't the law allow this poor man to end his?