In short, the meme's are used because people are getting sick and tired of very lazy people not taking the time to read even a few pages back to see if anyone else had asked the question.
Not only was the question asked today, but only "TWO" pages ago (Sunday) was the last time that the question was previously asked, and it was asked previously to that, only a couple of pages prior...
And as previously pointed out by Evil13, sometimes they ask the question immediately after someone else had asked it, and the question was answered, and not just with a meme...
So, very often, they can not even be bothered to read the things on that one page...
If people took the time to read the posts, or just use the search box in the top right side of the page, there would be no reason for the meme's to exist.
Reading is fundamental, and educational, because they can learn a lot along the way...