While I agree with the basic observation, that science as a process seeks upgrading while religion resists it, I want to take exception to the absolute way this has been expressed.
First, because empirically it has happened: Buddhism is an "upgrading" of Hinduism (as are Jainism and Sikhism), Judaism and Islam are "upgrades" on polytheism, and Christianity is an "upgrade" on Judaism. All of those were somewhat traumatic "revolutions" in folkways, but, as with the examples LanDroid gives, there are also gradual improvements going on most of the time.
Second, it is worth thinking anthropologically about these systems of beliefs. At their best, they are collections of almost disconnected insights, like the Biblical book of Proverbs or the I Ching. But occasionally some sage will receive a revelation, which is to say perceive a gestalt that organizes the folkways conceptually, and if those are taught and eventually written down, they exert a powerful influence on the thoughts of others, concerning how to live life. We have trouble resisting the magnetism of a conceptual structure that seems to make sense of complexity.
But because this gestalt comes with implications for our sense of right and wrong, it will be difficult to let it go once we have endorsed it. To forgo our sense of "why" certain things are right and others wrong is to risk moral disorientation, even chaos. The powerful pull of orthodoxy, with its strong attachment to structure, has been documented over and over. For me, that is the most important reason why religion resists upgrading.
There is another interesting aspect of the contrast, though. Science proceeds by fragmentation, that is, by focusing on increasingly specific aspects of reality in order to get better and better accuracy in description and understanding. Big conceptual structures ("paradigms," in Kuhn's terms), like the four humors or evolution or gravity or relativity, often link those specialized parts together, They illuminate which aspects of the specifics are most important.
Religion, by contrast, requires conceptual structures that deal holistically with life. At bottom, religion cannot tolerate "that was then, this is now," or "who is going to make me (respect others)?" because these fail to give a rationale for choices consistent with community life. Even the moral neutrality of Taoism is suspect, and its mystical insights have never really had a powerful influence because there is a massive disconnect between them and the exigencies of life in community.
Unfortunately, literal theism is the most economical way to express such a holistic narrative about why we should behave. There has never been a way to break down the big picture into smaller pieces and to focus on increased "moral accuracy" in specialized areas. Rather there is a constant tension between big picture moral truth and the pressures exerted by discrepancies of power. Might vs. Right is the rock on which moral systems keep foundering. And theism, with its ideas of judgment in the afterlife, solves the problem rather elegantly (but not with any descriptive intellectual integrity). Thus the tension in modernity between descriptive accuracy and religious structure is a tough one to resolve.
