You will get less letterboxing watching a 1.85:1 or 2.39:1 picture on a 16:9 display than you will on a 4:3 display - that's basic mathematics. Moreover, the entire TV industry is now geared to making 16:9 displays and the vast majority of new monitors are also 16:9. As a result, it is increasingly common for TV shows and websites to be designed for the widescreen format. So, tell me again how 4:3 is a better aspect ratio for tablets when the media you are likely to view on them is made with 16:9 formatting in mind?
Oh, sorry, you already answered that one, didn't you? "4:3 is better because Apple do it that way!"