All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
There is no doubt that the basis of superiority and honor in Islam is faith and piety as Allaah Says (what means): {O mankind, indeed We have created you from male and female and made you peoples and tribes that you may know one another. Indeed, the most noble of you in the sight of Allaah is the most righteous of you. Indeed, Allaah is Knowing and Acquainted.}[Quran 49:13]
Therefore, being a relative of the Prophet by itself is of no excellence, as Allaah announced to the uncle of the Prophet that he would be in Hellfire while he was still alive.
Nonetheless, if along with being a relative of the Prophet a person is pious and has faith (is a believer), then there is much virtue in this, and [all] bounty is in the Hand of Allaah; He grants it to whom He wills, and this bounty is clarified in the Sharee’ah and we must submit to it.
However, this honoring requires more obligations and duty, because a bad deed from the people of honor is not like a bad deed from any other person. Siddeeq Hasan Khaan said in his book ‘Fat’h Al-Bayaan’: “It is confirmed in this Sharee'ah in more than one place that the multiplication of honor and the increase of status necessitate for the person if he disobeys (Allaah) that his punishment is also multiplied.”
As regards why they (Ahlul Bayt) are not like all other Muslims, then it is because they are the closest kin (near relatives) of the Prophet and loving them is part of loving the Prophet ; it is for this reason that the Prophet himself said in the Hadeeth of Ghadeer Khum: “Whoever considers me as his Mawla (master), then Ali is his Mawla.” [Ahmad, At-Tirmithi and Ibn Maajah]
Allaah Knows best.