Relavant is also this post from our now dusty blog. For what it's worth, I would think that some of this is due to the growth of the site --- questions spend less time on the front page, and so have less time to be noticed and upvoted. However it is true that there are fewer upvotes than a year ago (yet much more than 2 years ago), so this explanation is at least incomplete, if not totally incorrect. — mixedmath ♦ 5 hours ago